Repair Zone Research Articles

Convenient Reparation of SiC-Coated C/C Composites by the Slurry Painting Method.

SiC-coated C/C composites with mechanical damage were repaired by the heat treatment method and slurry painting-preoxidation. The effects of different process parameters on the microstructure, interface bonding and oxidation resistance of Si-SiC repair coatings at 1773 K for 10 h were studied. The results show that the repair coating is tightly bonded to the original coating and the C/C substrate, and there is no obvious interface. Under the optimal parameters, the weight reduction in the repaired specimen merely amounted to 0.32% subsequent to oxidation at 1773 K for 10 h, and the mass loss was 74.79% lower than that of the damaged specimen, being proximate to that of the intact specimen. The objective of this work lies in achieving a greater density of the coating within the repair zone by manipulating the diverse powder ratios and preoxidation temperatures in the repair slurry, thereby safeguarding the C/C composite material against oxidation during its service. It offers a convenient and highly efficient approach for the repair of coatings with substantial size defects, significantly prolonging the service life of the material.

Microstructure and tensile properties of transient liquid phase (TLP) sintering repaired Ti–6Al–4V alloys with large area hole defect

Repairing defects in titanium alloy components is economically justified due to their high cost. In this work, Ti–6Al–4V samples with large area hole defects are repaired by transient liquid-phase sintering. The microstructure and tensile properties after repair have been investigated. The factors of different base powder morphology and the ratio of braze metal are also studied. The results show that by using spherical Ti64 alloy powder with 40 wt% TiZrCuNi braze alloy powder, an overall repair effect with high-density repair zone and good interface combination can be obtained at 960 °C for 3 h. The tensile strength of the as-repaired exceeds that of the matrix, but the elongation is lower than that of the matrix. Finally, the repair experiment conducted at various angles demonstrates this technique's strong practical feasibility.

Effect of vascularized jejunal conduit flap on peripheral nerve regeneration in rats.

In the literature, almost all of the nerve conduits proposed for obtaining better nerve recovery were applied as graft materials. In this study, we aimed to propose a new nerve conduit model with a flap pattern and evaluate the effect of a pedicled vascularized jejunal flap on nerve regeneration after wrapping it around a sciatic nerve. A total of 90 Wistar albino rats were randomly divided into nine groups with 10 rats in each. The first three groups constituted the control groups, whereas Groups 4-6 were the jejunum conduit (JC)-applied groups. A mucosa-resected JC (MRJC) was applied in Groups 7 and 8. Epineurial neurorrhaphy was performed in Groups 1, 4, and 7; repair with a nerve graft was applied in Groups 2, 5, and 8; and a 1-cm-long nerve defect was created in Groups 3, 6, and 9. After 2 months of follow-up, nerve regeneration was assessed by statistical analyses of the Sciatic Functional Index (SFI) and histopathological evaluation. The MRJC groups had significantly better results in terms of SFI (p = 0.005). Statistical differences in axonal degeneration, axonal density, myelination, and disorganization were found between all control groups and MRJC groups (p = 0.022, p = 0.001, p = 0.001, and p = 0.039, respectively). In this study, the feasibility of wrapping around the nerve repair zones of pedicled autologous flaps designed in a tubular fashion was observed in a small rat model. The findings must be further validated with larger animals before clinical testing.

Minimizing the landing zone of complex aortic repair using a physician-modified endograft to preserve a prominent Adamkiewicz artery

AbstractThere are increasing number of clinical cases with physician-modified endograft (PMEG) endograft for urgent reconstruction of large pararenal aneurysms to reduce the perioperative complication risks of fragile patients, but the risk of spinal cord ischemia due to the coverage of longer segment of thoracic aorta is relatively high.We demonstrate an expedited endovascular treatment of an 88 mm pararenal aneurysm by performing a 4-vessel fenestrated endovascular aortic repair. A prominent Adamkiewicz artery, ectatic supraceliac aortic segment, median arcuate ligament compression of the celiac artery and severe tortuosity of the common iliac arteries made the endovascular repair more challenging. A PMEG was implanted with simultaneous deployment technique to achieve a short proximal landing zone to preserve the Adamkiewicz artery.The proper risk assessment and preparation of the patient based on the clinical evaluation and procedure planning is essential for the clinical success of PMEG in urgent indication.

Study on Microstructure and Properties of LZ50 Axle Steel Repaired by Laser Additive Remanufacturing

ER308L stainless steel welding wire was used for laser repair of LZ50 train axle steel sample. A large number of defects, such as microcracks, pore shrinkage and porosity, can be found in the re-manufacturing sample. A wave-like structure was formed at the boundary of the fusion zone between the augmented repair material and the base material, and the structure in this zone was consist of about 83% martensite and about 17% austenite, In the ER308L stainless steel welding wire repair zone, columnar equiaxed crystals with different lengths and morphology were formed, all of which pointed to the center of the molten pool. After repair, the tensile strength of the specimens decreased from 601.34MPa to 427.81MPa, and the elongation decreased from 16% to 5%, The fracture mode was a combination of ductile fracture and brittle fracture.

Solid-state friction rolling repair technology for various forms of defects through multi-layer multi-pass deposition

The current Friction Stir Welding (FSW) based solid-state defect repairing method is an ideal repair technology for high-strength aluminum alloy. However, due to the limitation of pin length and the existence of shoulder, the stirring pin cannot penetrate deep into the root of defects and is difficult to extend in the width direction, which poses great challenges for components with large defects, such as one-dimensional, two-dimensional and volume defects. To overcome these limitations, this study successfully achieved effective repair of various forms of defects using the solid-state Friction Rolling Repair (FRR) technology through multi-layer multi-bead deposition. The microstructure and mechanical properties of the repaired ZL114A cast aluminum alloy joints were investigated. The results demonstrate well-bonded repaired boundaries, significant grain refinement at the junction between the repaired area and boundary, and ultimate tensile strength exceeding 80 % of base material strength. The average grain size of the repaired area can reach a minimum of 2.82 μm. The grain refinement degree of the side joint of the surface defect repair sample is higher than that of the bottom joint, and the corner joint of the bottom surface shows the highest proportion of recrystallized grains. Fracture locations were consistently within the interior of the repair zone in tensile specimens, indicating superior properties at side joints compared to those within the interior. The research proves that FRR has the ability to repair a variety of typical defects, including one-dimensional, two-dimensional and volume defects, in the process of processing and service, which lays a foundation for the industrial application of FRR.

Toward developing remanufactured Ti6Al4V alloys with high fatigue crack growth resistance by in-situ cooling during laser remanufacturing

The fatigue performance of remanufactured titanium alloy blade components has garnered significant attention in recent years. The repaired titanium alloy components using the direct energy deposition (DED) method exhibit structural differences, leading to an inhomogeneous microstructure that directly impacts the service life of the remanufactured component. The work presented here aimed to investigate novel approaches for enhancing the resistance to crack propagation and to gain a deeper insight into the fatigue crack propagation characteristics of the Ti6Al4V remanufactured interface with an inhomogeneous microstructure. The research focused on analyzing the microstructure evolution and fracture properties of remanufactured components using in-situ cooling. The results indicate that in-situ cooling has the potential to decrease the anisotropy of the repaired zone (RZ) and enhance the resistance to crack propagation in the heat-affected zone (HAZ) and base metal (BM). The high cooling rate associated with the in-situ cooling can elevate the presence of high-angle grain boundaries (HAGBs) in the RZ, diminish the phase transformation between the HAZ and BM, and decrease the size of the secondary α phase. The research contributes to a deeper comprehension of fatigue crack propagation in remanufactured components and provides a pathway for the improvement of fatigue performance of remanufactured titanium alloy.

Internal mammary artery perforator flap for repair of an upper thoracic tracheo-oesophageal fistula

Tracheoesophageal fistulas (TOF) following esophagectomy for esophageal cancer are rare but potentially fatal. There is no consensus on treatment between stenting and surgical repair, although the latter is associated with better distant survival. In surgical repair, the interposition of a flap improves healing by providing well-vascularized tissue and reinforcing the repair zone. The flaps described are usually muscular and decaying. We present the case of a malnourished fifty-year-old man who underwent intrathoracic surgical repair of symptomatic recurrent TOF using a skin flap based on the perforators of the internal thoracic artery (IMAP). The perforator flap was completely de-epidermized and tunneled under the sternum by a proximal and limited resection of the 3rd costal cartilage and placed at the posterior aspect of the trachea, with the excess tissue rolled up on either side. At 9 months, the patient showed no recurrence and improved general condition. The de-epidermized IMAP tunneled under the sternum intrathoracically is a reliable alternative to the conventional muscle flaps described in TOF management and an attractive additional tool in the plastic surgeon's surgical arsenal.

Enhancing the tensile properties of laser repairing Ti-6Al-4V alloys: Optimization of strain distribution based on composition fine-turning

In the context of laser repairing damaged forging titanium (Ti) alloys, a common challenge is the significant reduction in elongation of the repaired samples compared to that of the substrate. In this work, directed energy deposition (DED) technology was employed to repair the TC4 (Ti-6Al-4V) forgings by manipulating the Al and V contents of the repaired zone (RZ). Subsequent evaluation encompassed the microstructure, microhardness, and tensile properties across the laser repair deposition samples (LRDs). The results revealed that despite the LRD TC4–0Ti's strength reaching 97.80% of the substrate, its elongation is only 43.93% of the substrate. Upon appropriately reducing the Al and V contents of RZ, the LRD TC4–5Ti demonstrates a strength of 935.04 MPa and an elongation of 14.59%, achieving 98.70% and 82.38% of the substrate, respectively. As the Al and V contents of RZ are further decreased, the strength of the LRDs gradually diminishes, falling below the forging standards. Utilizing digital image correlation (DIC) technology, the deformation behavior of different zones during the tensile process of these LDRs was investigated. The results indicated a concentration of strain distribution within either RZ or the substrate zone (SZ) of the LRDs during the tensile process, which signifies the mismatch of deformation capacity between these two zones. Consequently, the tensile properties of the LRDs were adversely affected. By judiciously adjusting the Al and V contents of RZ, the abovementioned mismatch phenomenon can be ameliorated, which facilitates a synergistic strain behavior between SZ and RZ during the tensile process, aiding in the homogenization of strain distribution and consequently enhancing the tensile properties of the LRDs.

Study on fatigue crack growth behavior of the TA15 titanium alloy repaired by laser deposition

Laser deposition repair was employed to repair the body and surface of the forged TA15 titanium alloy. Subsequently, the fatigue crack growth behavior of the repaired components after annealing was investigated. The results showed that the fatigue crack growth rate (FCGR) of the body-repaired specimen decreased from the initial cracks in the heat-affected zone (HAZ), interface, and repaired zone (RZ). The increase in the repair layer thickness drastically reduced the FCGR in the surface-repaired specimen. The main crack growth mode was crossing the primary α and transformed β in the substrate zone (SZ), primarily crossing the lamellae α and along lamellae α in the HAZ, and crossing the lamellae α in the RZ. The RZ developed a tighter bond with the substrate interface, making crack growth more difficult. Crossing the lamellae α in the basket-weave structure required higher amount of energy and exhibited significant increase in tortuosity. Hence, the FCGR of the initial crack within the RZ exhibited the lowest rate. An increase in the thickness of the repair layer increased the proportion of the basket-weave, improving the resistance against crack growth, and increased the tortuosity associated with the crack path, reducing the FCGR. It was confirmed that the proposed body and surface repair methodology improved the FCGR of investigated specimens.

Land inventory and designation of the Kranji river riparian zone in Purwokerto city, Central Java

River banks are virtual lines of the riverbed designated as river protection boundaries. This research aimed to inventory the Kranji Riverbank’s land condition and conduct a study to determine the width of the riparian zone. The methods used were field surveys, identification of land along the 11 km river, and analysis of flood discharge designs with a return period of 10 years. The results of an inventory along the river on the river land dominated the permanent building. There are 400 building units included in the repair zone on the Kranji River. Based on the planned flood analysis results with a return period of Q10 years of 38.11 m3/s, there are 160 flood points along the river. The width of the riparian zone in urban areas is 10 meters in East Purwokerto, while outside urban areas, it is 50 meters in Baturaden District. The benefit of the results of this research is the provision of initial data for coordinating with several other agencies in efforts to implement the Kranji River border in the future.

Artificial Intelligence and Our Secret Mind: Human Mediation in Grey Zones

CIRET has set up an AI research group to highlight the need for human ethical mediation in theage of digital technology and binary logic. Francisco Varela has observed that cognition can take place inthe computer field without appealing to consciousness. Yet human decision-making cannot be the resultof cognition alone and requires the interaction between cognition and consciousness. In fact, rationalistand reductionist models borrowed from the hard sciences have only shown a mechanistic vision of AI ora biological-environmental vision, which cannot be applied to complex human phenomena occurring in agrey zone. In this grey or fuzzy zone of mediation, conciliation, and repair, we need the dialectical processor dialogue between consciousness and cognition. In this context, the proposal of mediating leaders andmanagers appears as a possible ethical alternative to demonstrate that consciousness is beyond the logicof the computer. Humans must remain responsible for all the effective decisions that will help us solveproblems theoretically and concretely. We therefore need an emerging global wisdom that flows from ourconversations about AI and appeals to human consciousness at all its levels of reality. This group produceda Symposium on November 21 and 22, 2023, in which we imagine that AI may be at the service of humanevolution and resiliency in “learning to be societies” instead of contributing to block our evolutions: if AIremains a work tool. . . Certainly it will because the creation sparkles still a mystery for men themselves.

A study on the effect of weld repair on the structural margins of a solid rocket booster hardware

Cylindrical shells in one of ISRO’s solid rocket booster is fabricated from ultra-high strength steel (M250 Maraging steel) through rolled and welded construction. This steel being a fracture prone material, elastic-plastic fracture mechanics-based design is followed for the design of cylindrical shell. The no-flaw failure pressure i.e. elastic plastic failure pressure (Pb) of the cylinder is an important parameter in design. For a given diameter of cylindrical shell, Pb is a function of shell thickness and mechanical property. If any unacceptable flaw is found on welds during NDT, repairs are carried out in the weld region. Mechanical properties of weld/weld repairs are lower when compared to parent material. It is seen that, at any location, if it is repaired twice, the strength reduces by 21% when compared to the parent metal property. Thus, the mechanical properties of the weld region dictate the overall design thickness of the cylindrical shell. A study is carried out to find the effect of length of weld repair zone on the Pb. A parametric 3D FE model simulating the repair in long seam weld, cirseam weld and combination of long seam & cirseam weld in cylindrical shell is used for this purpose. It is found that the effect of parent metal property needs to be considered while estimating Pb. Further while considering the repair in long seam, the length of repair also needs to be considered. Pb is found to increase considering its effect. This study was helpful in establishing more realistic structural margins in a solid rocket booster case which had weld repair.

Intramural hematoma in the proximal sealing zone of the thoracic endovascular aneurysm repair: frequency and safety in acute and subacute type B dissections.

To assess the outcomes after thoracic endovascular aneurysm repair (TEVAR) in the presence of intramural hematoma (IMH) in the proximal sealing zone. Patient data were retrospectively extracted from the hospital records of patients treated with TEVAR for acute and chronic aortic dissection type B in one single center. The initial, preoperative, first postoperative, and last follow-up CT scans were evaluated in the aortic 3D multiplanar reformats and the centerline regarding IMH presence in the proximal sealing zone, anatomical preconditions, and the morphological TEVAR complications including migration and bird-beak. Groups with (IMH) and without IMH (no-IMH) were compared. Overall, 84 patients (IMH:42; no-IMH:42) were treated at the age of 63(55; 72) years, of whom 23/84 (27%), 34/84 (40%), and 27/84 (32%) were in the hyperacute, acute and subacute dissection phases, respectively. The bovine arch was found in 10/84(12%) and the type III arch was most common (43/84;51%). IMH maximum extent was found in zones 0, 1, 2, and 3 in 14/84 (17%), 17/84 (20%), 18/84 (21%), and 6/84 (7%), respectively. Sealing was achieved in zone II in 71/84 (85%) and LSA was revascularized in 66/84 (79%) of the overall cohort. Early mortality and paraplegia were 2/84 (2%) each; stroke rate was 3/84 (4%). During the 22 months median follow-up (22;4;43) no RTAD was observed. Migration ≥10 mm (IMH: 11/82; no-IMH: 10/82; P = 1.0) and bird-beaks (IMH: 10/82; no-IMH: 12/82; P = 0.8036) were comparable in both groups and accompanied by a low aorta related mortality (1/82) in both groups. The presence of the IMH in the proximal TEVAR sealing zone is frequent and may not be relevant for the occurrence of the RTAD, stent-graft migration, or bird-beak formation.

4 A Quantitative Image Analysis Study of Modified Kessler Extensor Repair

Abstract Aim The aims of this study were to compare and measure the amount of 4.0 Prolene suture material at the tendon repair site with 2 types of knot placement in a modified Kessler technique, as placement of suture knot can impact extensor tendon healing. Method Thirty-two extensor tendons of 2 fresh frozen cadaveric hands were divided and repaired using the modified Kessler technique with either intratendinous or extratendinous knot placement of a 4.0 Prolene suture. Tendon repairs were sectioned, and cross-sectional photographs were analysed using quantitative image analysis. Results Comparison of percentage change in tendon dimension surface area showed no significant difference (p = 0.4750) between intratendinous and extratendinous knot placement to demonstrate consistency of repair. Quantitative image analysis revealed suture material occupied a significantly (p = 0.0103) larger percentage of tendon cross sectional area in intratendinous than extratendinous knot placement. In both groups this represented <10% of the total cross-sectional area of the tendon at the repair site (7.49% vs 2.92%). There was no significant relation between digit, tendon or repair zone and percentage of repair zone occupied by suture material. Conclusions Intratendinous knot placement occupies a larger proportion of tendon cross sectional area than extratendinous knot placement, though this is still comparatively small when a 4’0 monofilament suture is used.

Evaluation of the ATI 718Plus repaired by laser metal deposition under heat treatment regimes: Microstructures, mechanical properties, and their heterogeneity

Laser metal deposition (LMD) is an attractive repaired technology for integral impellers and blades. After maintenance, the LMD usually generates an inhomogeneous microstructure joint consisting of two zones: repaired zone (RZ) is mainly composed of highly textured columnar dendrite and long striped Laves phases in the inter-dendrite, while the substrate zone (SZ) displayed equiaxed grains with rod-like η phases on grain boundaries. RZ is the limiting factor due to the absence of γ′ and the presence of Laves phase. Three specific heat treatment regimes, namely direct aging (DA), solution and aging (SA), and homogenization and aging (HA) were chosen to investigate the microstructure response of heat treatments including the grain size, Laves phase, η phase, and γ′ phase of RZ and SZ. After heat treatment, the mechanical compatibility was highly improved, and the global tensile properties were analyzed based on the microstructure evolution and respective tensile properties. The tensile properties of the DA and SA joint reached the same level of wrought ATI 718plus alloys, whereas the ductility is lower due to the inhomogeneous deformation. Comparatively, the HA sample showed higher ductility and lower strength due to abnormal grain growth.

Abstract P1080: Periostin Is Induced During Cell-based Repair In The Sheep Model Of Myocardial Infarction

Cardiac disease is the leading cause of death worldwide. Stem cell-based therapy may improve patient outcomes following a myocardial infarction. Our laboratory is studying the mechanistic basis by which neonatal Islet-1 positive cardiovascular progenitor cells (CPC) facilitate post infarct repair in the sheep model of myocardial infarction. Here, we addressed the hypothesis that periostin (POSTN) is induced in the cardiovascular repair zone following neonatal Islet-1+ cell-based repair. POSTN promotes cardiomyocyte proliferation, recruitment of M2 macrophages, epithelial-mesenchymal transition (EMT), migration, and angiogenesis. We examined human neonatal Islet-1+ cardiovascular progenitor cell clones isolated from several patients to initially determine whether or not POSTN was expressed in these cells. All clones expressed POSTN as shown by RT-PCR. The size of the amplified transcripts was confirmed by gel electrophoresis and POSTN expression in these clones was further confirmed by RNA sequencing. We then examined POSTN expression in the cardiovascular repair zone following myocardial infarction and cell transplantation in sheep. Sheep neonatal Islet-1+ CPC clones were used in this model of allogeneic cell-based repair. A myocardial infarction was induced in three Western sheep by left anterior descending coronary artery ligation. Ten million neonatal sheep Islet1+ cardiac progenitor cell clones isolated from 9 day old sheep were injected into the area surrounding the infarct site 3-4 weeks post infarction. RNA was isolated from the cardiovascular repair zone two months after cell injection. The non-infarcted region of the left ventricle and the left ventricle of normal, non-infarcted sheep were used as controls. POSTN transcripts were significantly elevated in the cell-treated cardiovascular repair zone of all three sheep, as identified by qRT-PCR relative to controls. Periostin levels were elevated between 6 and 255 fold in the repair zone relative to the non-infarcted region of the heart. Our data shows that POSTN is expressed in human Islet-1+ neonatal cardiovascular progenitor cells and that POSTN levels are induced during cell-based cardiovascular repair in the sheep model of myocardial infarction.

Poster 256: Pediatric Meniscus Repair: Safety Profile based on > 2000 Arthroscopic Meniscus Repairs

Objectives: Pediatric meniscus tear prevalence is increasing, and meniscus preservation methods are essential for long term knee function in this at risk group. In this patient population meniscus anatomy and vascularity may support higher rates of healing after repair, but safety of meniscus repair has not been studied in a large prospective cohort group. The purpose of this study is to establish the incidence of complications associated with pediatric meniscus repairs in a multi-center prospective quality improvement registry, and to identify the characteristics of meniscus repair that are associated with complications. Methods: A prospective multi-center quality improvement registry (16 institutions, 26 surgeons) monitoring the safety of meniscus repairs was reviewed. Audit processes using CPT codes were designed to ensure that all consecutive cases were prospectively entered on patients <19 years old into a HIPAA- compliant electronic platform. Each meniscus repair case with a complication form was secondarily reviewed to ensure consistency of identification and grading according to the modified Clavien Dindo classification. Demographics, tear type, repair technique, and implant type, when applicable, were included, and a common cause analysis was performed to evaluate risk factors for early repair failures. Results: 2375 meniscus repair cases were identified, with a mean age of 15.1 years (2-19) and 44.1% females. These consisted of (25%) isolated repair, (5.4%) discoid meniscus repair, and (66.9%) concomitant ACL and meniscus repair. Overall complication rate was 12.64%, with 5.67% grade III complications. The most common complications were motion loss/stiffness (3.96%), failed repair (2.3%) and continued pain/mechanical symptoms (2.09%). Failed repair was identified in all repair groups but had the highest prevalence in isolated meniscus repair (6.38%), in which grade III complications were more common overall. Stiffness was more common when a meniscus repair was performed during an ACL reconstruction (2.1% Grade II and 1.27% Grade III). There was no statistical difference in complications associated with age, gender, or technique, medial or lateral meniscus, displacement, or zone of repair. However, posterior horn and posterior horn + body repairs of the medial meniscus sustained more complications (p=0.003) as did longitudinal/complex tears of the lateral meniscus (p=0.02). Conclusions: Pediatric meniscus repairs performed arthroscopically have a complication rate of 12.64%, with 1 and 20 meniscus repairs leading to a grade III complication. Although there is no difference in complications based on technique, posterior horn medial meniscus and longitudinal tears of lateral meniscus may be at higher risk of complications.

Impact of spray angle and particle velocity in cold sprayed IN718 coatings

Cold spray (CS) deposition has potential applications in repair technology or additive manufacturing due to its ability to operate at low temperatures, achieve high deposition rates, and produce thick, dense coatings. For adoption of CS in repair applications, it is crucial to evaluate the influence of spray angles since geometry of repair zones are typically complex and non-flat. In this work, we investigated the influence of spray angles and particle velocities on the cold spray deposition of Inconel 718 (IN718) powder particles using N2 as propellant gas. Three oblique spray angles including 50, 60 and 70° were compared with the 90° normal spray angle for cold spray deposition of IN718 powders on Al6061 substrate. Three sets of cold spray parameters at each spray angle, giving particle velocities from 820 to 920 m/s were employed to study their effect on the coating properties. Particle velocity was found to have greater impact on coating porosity compared to spray angle. Coating with lowest porosity and lowest surface roughness but highest compressive surface residual stress was achieved with deposition at lowest spray angle (50°) and highest particle velocity (920 m/s). Changing the spray angle has greater influence on the deposition efficiency, with thickest coating observed at normal spray angle of 90° across all three cold spray conditions. Finite element method (FEM) simulations were also performed to understand the influence of powder and substrate temperatures on critical angles for bonding. The simulation results suggest that elevating the powder temperature is likely to cause a slight increase in the critical bonding angle.

Research on the Microstructure and Mechanical Properties of Repaired 7N01 Aluminum Alloy by Laser-Directed Energy Deposition with Sc Modified Al-Zn-Mg

Aluminum alloy is an important material used in railway train structures. It is of great significance to repair aluminum alloy through directional energy deposition to reduce cost and improve the performance of the aluminum alloy. In this study, 7N01 aluminum alloy was repaired by means of laser-directed energy deposition (DED) with the powder of Sc-modified Al-Zn-Mg aluminum alloy as raw material. The microstructure and mechanical properties of the repaired specimens were studied through the metallographic microscope, scanning electron microscope, electron backscatter diffraction, universal tensile test, and Vickers hardness test in combination. The results show that the bonding interface of the repaired aluminum alloy is satisfactory, and the porosity is 2.8%. The grains in the repaired area are the columnar crystals growing vertically along the boundary of the melt pool with an obvious temperature gradient. Fine equiaxed crystals are distributed along the boundary of the melt pool, and Al3(Sc,Zr) particles play a role in grain refinement. The average grain size of the fine grain area in the repair zone next to the fusion zone is 9.1 μm, and the average grain size of the coarse grain area is 20 μm. The average tensile strength in the area of repair approaches 349 MPa, which is 91% that of the base material, and the elongation rate is 10.9%, which is 53.2% that of the base material. The hardness ranges between 122 HV and 131 HV, which is comparable to the base material. However, there is a significant decrease in the tensile strength and hardness of the base material (heat-affected zone).