Mg2Si Phase Research Articles

Effect of heat input on microstructure and mechanical properties of AA6061 alloys fabricated by additive friction stir deposition

Heat input (HI) is the major factor that affects the surface quality, microstructure and mechanical properties of the deposition during the additive friction stir deposition (AFSD) process. Effect of HI on the microstructure and mechanical performance of the AFSDed AA6061 has been in-depth explored via adjusting the values of traverse speed (v) and layer thickness (t). Results indicate that deposition with a higher HI promotes the material flow behavior as well as the plastic deformation, which effectively enhances the grain refinement and structural uniformity, and avoids the formation of defects. Meanwhile, TEM results confirm that the enhanced HI leads to the formation of a higher volume fraction of the finer precipitations (Mg2Si and AlFeSi phases), which assists in suppressing abnormal grain growth phenomenon and improves the bonding strength of the deposition. As HI decreases, the transfer efficiency of materials clearly reduces because of the incompletely softened materials, causing less plastic deformation and poor interlayer bonding strength of the deposition. The deposition with the lowest HI displays the worst tensile properties with the lowest micro-hardness (107 HV0.5), YS (273 MPa) and UTS (303 MPa).

Effect of neodymium on microstructure, mechanical properties, and corrosion behavior of Mg-2Si-xNd alloys fabricated by powder metallurgy

In the present work, the effects of neodymium (Nd) on microstructure, mechanical performance, and corrosion behavior of powder metallurgy Mg-2Si-xNd (x = 0.05 wt%, 0.15 wt%, and 0.20 wt%) alloys were investigated. Microstructures were examined by optical and scanning electron microscopes combined with an energy-dispersive spectrometer. Hardness and compressive tests were used to study the mechanical properties of alloys. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis, and the hydrogen evolution test were applied to characterize the corrosion behavior of alloys in Hanks’ solution. The microstructure of Mg-2Si-xNd alloys mainly consists of α-Mg matrix, Mg2Si, and MgNd phases. The increase in Nd content tends to decrease the aspect ratio of α-Mg grains, which leads to the enhancement of the ultimate-compressive strengths and hardness of the alloys. Potentiodynamic polarization shows that increasing Nd content leads to a lower corrosion current density in the Mg-2Si-xNd alloys. The EIS results confirm that a higher addition of Nd suppresses the dissolution kinetics of the alloys due to the increasing charge transfer resistance. Mott-Schottky analysis reveals the formation of an n-type semiconductive passive film on the alloy surfaces, where the interstitial and oxygen vacancies predominate over the metal vacancies. The X-ray photoelectron spectroscopy (XPS) reveals that a mixture of Mg(OH)2, MgO, MgCO3, and Nd2O3 has formed as the corrosion products on the Mg-2Si-xNd alloy surfaces after a longer immersion time in Hanks’ solution.

Effect of trace Bi addition on the microstructure and mechanical properties of hypoeutectic Al-Mg-Si-Mn alloy

The effects of Bi on the eutectic structure and mechanical properties of AlMg5Si2Mn alloy were investigated. The results show that when trace Bi is added to the alloy, the eutectic Mg2Si phase in the alloy is successfully refined from long plate-like to fine fiber rod-like and coral-like structure. It is mainly attributed to the precipitation of Bi atomic clusters on the front of the solid-liquid interface and form a component supercooling, in which part of Bi atoms react with Mg atoms to form nanosized Mg3Bi2 particles, which effectively inhibits the rapid growth of eutectic Mg2Si and promotes the branching and refining of eutectic Mg2Si. The strength and ductility of AlMg5Si2Mn alloy containing Bi are significantly improved simultaneously. Compared to the unmodified alloy, the largest tensile strength, yield strength and elongation to failure of the 0.3wt % Bi-modified alloy are increased to 28.04%, 12.3% and 129.1%, respectively. The fracture mode of the alloy changes from brittle fracture to ductile fracture.

Influence of Gas Oven Temperature on the Microstructure and Extrudability of Al-Mg-Si Aluminium Alloys

The microstructure of Al-Mg-Si aluminium alloys is well characterised when it comes to the initial state of the cast billet or the artificially aged profile. Typically, a gas oven coupled with an induction oven is used to preheat the billets before extrusion. Preheating reduces the flow stress of the aluminium and dissolves the phases that have precipitated during cooling after homogenisation. In this paper, the influence of the gas oven temperature on the partial or complete dissolution of the precipitated phases will be shown. In addition, the negative effect of a wrong choice of parameters on the volume content of the MgSi phases will be shown.

An investigation on effect of tramp elements and solidification processing on homogenization kinetics of AA 7xxx series aluminum alloys

AA 7068 Aluminum alloy is produced via conventional solidification (CS) and controlled diffusion solidification (CDS) processing and homogenized at 450 °C for 6 and 12 h. Optical microscopy (OM) and scanning electron microscopy (SEM) equipped with an energy dispersive x-ray spectroscope (EDS) were used to examine the as-cast and homogenized samples. It was found that although the CS sample is more chemically homogenized in the as-solidified state, the CDS sample exhibits a higher homogenization rate during the treatment. The calculated phase diagram (CALPHAD) methodology was employed to study the effect of silicon and iron on the solidification path and homogenization of the alloy. Silicon consumes magnesium atoms on the surface of the α-Al phase to form the Mg2Si phase. Therefore, the magnesium concentration on the α-Al phase required for the formation of the σ phase must be increased. Calculations shows that all the Mg atoms at this stage are completely supplied from the bulk of the αAl phase. It can be hypothesized that during the last stage of solidification, a solid/liquid diffusion couple can be created between the primary αAl and the remaining liquid for several minutes (4 min at a cooling rate of 0.2 oC/s). As a result of the activation of this couple, the Mg atoms diffuse from the α-Al bulk to its surface, and vacancies diffuse from the surface to the bulk, forming a line of Kirkendall voids. With CDS processing, the surface of the primary phase is less Mg-concentrated than that in the CS process and this significantly reduces the formation of the Mg2Si phase. Conversely, the vacancy and Mg concentration of the αAl phase in CDS is higher than that of CS and this lets other alloying elements other than Mg diffuse to the primary phase, decreasing the homogenization time. The presence of Si in the alloy leads to the formation of the Mg2Si phase, which significantly reduces the final Mg concentration in the α-Al phase after full homogenization. In the pure alloy, the Mg concentration is 2.42 wt%, while in the FeSi-containing alloy, it is reduced to 1.58 wt% due to solid solution and dispersion strengthening mechanisms. Through CDS processing, the negative impact of Si can be reduced by disrupting the mechanism of Mg2Si formation.

Effect of Mg on the Microstructure, Mechanical Properties, and Surface Roughness of Functionally Graded A413 Composite: Machine Learning Approach at Wire‐Cut Electric Discharge Machining Zone

The present study assists the industrial sectors by implementing low‐weight high‐strength aluminium composite. The pristine magnesium as a reinforcement in three different weight percentages (3.5, 7, and 10.5) is utilized to fabricate the A 413 composite using centrifugal casting. The density analysis concludes a higher level of Mg inclusion prompts the material to save 3.9% of weight. Microstructural study of centrifugal casting specimens reveal a rich existence of hard phase Mg2Si in the outer zone, with its richness decreasing toward the inner zone. The tensile test result affirms the functionally graded nature of the material with the increasing trend of tensile strength from the inner to the outer. Fractured surface analysis concludes the existence of cracks and their propagation for the inner region specimen. The influence of magnesium on the surface finish of functionally graded composite at the wire cut electric discharge machining (WEDM) zone is predicted using a machine learning‐based random forest regressor (RFR) algorithm. The supervised learning algorithm declares that 10.5 wt% of Mg facilitates the minimal surface roughness of 0.229 µm with the optimal combination of parameters 6 A of current, 115 µs of pulse‐on time, 60 µs of pulse‐off time, and 8 N of wire tension.

Improvement of mechanical properties of Mg2Si phase system by doping transition metals: a first-principles study

Improvement of mechanical properties of Mg2Si phase system by doping transition metals: a first-principles study

Flow behavior and microstructural evolution of Al-1.2Mg-2.4Si-1.2Cu-0.6Mn alloy during hot compression

Thermal compression tests were conducted on Al-1.2Mg-2.4Si-1.2Cu-0.6Mn alloys with process parameters including deformation temperatures ranging from 400°C to 550°C and strain rates ranging from 0.05 s⁻¹ to 1 s⁻¹. The hot working properties of aluminum alloys were evaluated with intrinsic equations and machining diagrams. The results show that the processing safety zones of the alloy are 425–450℃ and 0.05–0.1 s−1, 450–475℃ and 0.1 s−1-0.5 s−1, and 475–500℃ and 0.5 s−1. The microstructure of the aluminum alloy following hot pressing was investigated through the use of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and backscattered electron diffraction (EBSD). When the deformation temperature of the alloy is below 450°C, the alloy organization exhibits a greater prevalence of inhomogeneous defects, which manifest as coarser granular regions in the micro-morphology. Upon reaching a deformation temperature of above 525°C, the deformed alloy organization exhibits an evident thermal cracking phenomenon. At the same temperature, an increase in strain rate is accompanied by a decrease in the Mg2Si phase and an increase in the precipitation of the Al(Fe,Mn)Si eutectic phase. Furthermore, the precipitated phase tends to become coarser. The presence of certain Mn-containing nanoparticle dispersions can impede the migration of subgrain grain boundaries, while simultaneously pinning dislocations and accelerating the generation of dislocation entanglement. This also can serve to inhibit the coarsening of the grains to some extent.

The Influence of Post-Treatment on Micropore Evolution and Mechanical Performance in AlSi10Mg Alloy Manufactured by Laser Powder Bed Fusion.

Gas-induced porosity is almost inevitable in additively manufactured aluminum alloys due to the evaporation of low-melting point elements (e.g., Al, Mg, and Zn) and the encapsulation of gases (e.g., hydrogen) during the multiple-phase reaction in the melt pool. These micropores are highly unstable during post-heat treatment at elevated temperatures and greatly affect mechanical properties and service reliability. In this study, the AlSi10Mg samples prepared by LPBF were subjected to solution heat treatment at 560 °C for 0.5 and 2 h, followed by artificial aging at 160 °C, 180 °C and 200 °C, respectively. The defect tolerance of gas porosity and associated damage mechanisms in the as-built and heat treated AlSi10Mg alloy were elucidated using optical, scanning electron microscopic analysis, X-ray micro computed tomography (XCT) and room temperature tensile testing. The results showed the defect tolerance of AlSi10Mg alloy prepared by LPBF was significantly reduced by the artificial aging treatment due to the precipitation of Mg-Si phases. Fracture analysis showed that the cooperation of fine precipitates and coarsened micropores assists nucleation and propagation of microcracks sites due to stress concentration upon tensile deformation and reduces the tensile elongation at break.

Microstructural evolution and precipitation behavior of multicomponent Al83Mg5Si5Cu5Li2 alloy

We investigated the microstructural evolution and precipitation behavior of a new multicomponent Al83Mg5Si5Cu5Li2 alloy using transmission electron microscopy and atom-probe tomography. As-cast alloy consists of θ-Al2Cu, Mg2Si, Q-Al5Cu2Mg8Si6, and AlLiSi phases. Solution treatment causes the formation of the Q-Al5Cu2Mg8Si6 phase, and slow furnace cooling causes the formation of θ-Al2Cu particles in the Al matrix, which depletes solute atoms. Nanoscale Cu/Si/Mg-rich solute clusters are formed during natural aging, contributing to an excellent age-hardening response.

Development of Aluminum Alloys 6061(AA6061) Silicon Carbide (SiC)-Graphite (GR) and Hybrid Composite for Automotive Applications

The microstructure and mechanical properties of composite materials made of Silicon carbide (SiC) and Graphite (GR) reinforcement, known as Aluminum Alloy 6061(AA6061) Matrix were developed. Using the stir casting method, the hybrid composites were prepared with 6 weight percent of the reinforcements in the ratio of 0:1,1:3,1:1,3:1,and 1:0. It was determined how the reinforcement particles affected the microstructures and mechanical characteristics of these materials. The microstructure displays a uniformly distributed fine particles of α-Al grains and Mg2Si phase with in the matrix alloy. The microstructure amply demonstrates the presence of the reinforcing particles (SiC and GR) and dendritic development was noted. There are very few indications of particles clusters, and the particles are very dispersed throughout the matrix. Sample A2 (AA6061 25% SiC/ 75% GR) had the highest recorded hardness value of 123.34 HRB4.8,9.33, while the base alloy had the lowest value of 70.36 HRB when compared to the base alloy, the developed hybrid composites showed improved tensile strength. In contrast to the base alloy, which displayed a strength of 115.67N/mm2, Sample A3 demonstrated a maximum strength of 143.88 N/mm2 as compared to the base alloy which showed strength of 115.67 N/mm2. The hard reinforcement particles sharp edges serve as a nucleation site, which is why the strength of samples A4 and A5 decreased when SiC reinforcement is added, the materials extension decreases when the developed hybrid composite materials with samples were compared with the base alloy. In comparison to the created hybrid composite materials, the base alloy displayed a maximum extension of 2.4mm, with sample A5 showing the lowest extension value of 1.23mm. Sample A2 displayed the highest structures rate of 0.060, while sample A5 displayed the lowest strain rate of 0.031. The impact strength values increases from 2.76 (Base alloy) to 4.77j (Sample A5) with the addition of the reinforcement particles. The obtained mechanical properties indicate that the reinforced alloy performed favorably well but not significantly better than the ones in the literature.

The electrochemical corrosion performance of aluminum alloys grade 6082-T6 weld repair

This research investigated the corrosion behavior of standard current metal inert gas weld repair for 6082-T6 aluminum alloy using ER5356 filler metal. The new and repaired (NW and RW) welds were studied. The welds comprised the weld metal (WM), the heat affected zone (HAZ) (solid solution and softened zones), and the base metal (BM). The study focused on investigating electrochemical corrosion using polarization and electrochemical impedance spectroscopy (EIS) methods in 3.5% NaCl solutions, especially in HAZ, including metallurgical and mechanical examinations. The BM containing an α-Al matrix with Al(Fe,Mn)Si and Mg2Si phases exhibited the maximum hardness (70–104 HV0.1). The WM hardness decreased (67–76 HV0.1) with the α-Al, β-Mg3Al2, and Mg2Si phases. Despite having comparable phases to BM, HAZs showed lower hardness (Solid HAZ: 70–82 HV0.1) due to more intermetallic phases. The RW’s softened HAZ revealed the minimum hardness (52–63 HV0.1) compared to that of the NW (55–70 HV0.1). Besides, the tensile strength of the RW (179.7 MPa) was also lower than that of the NW (174.4 MPa) because of the reheating effect. The electrochemical corrosion results indicated that the BM exhibited the maximum corrosion resistance (the lowest corrosion current density (icorr), the highest corrosion potential (Ecorr), and the charge transfer resistance (Rct)), followed by the HAZ and the WM, respectively. The softened HAZ demonstrated better corrosion resistance than the solid solution HAZ. Conversely, the over-aging effect reduced the softened zone’s pitting corrosion resistance (Ep) compared to the solid solution zone. The RW exhibited inferior corrosion resistance compared to the NW due to increased intermetallic phases, which was consistent with the mechanical results. However, the RW’s softened HAZ corrosion characteristics were inconsistent with its mechanical properties; its hardness and tensile strength were the lowest, but its corrosion resistance was not. Pitting corrosion was observed on the weld surfaces using the SEM.

Modification and strengthening of recycled Al-Mg-Si-based alloy upon continuous rheological extrusion (CRE) forming

With global warming and resource scarcity, it is crucial to devise a simple, energy-efficient, and low-emission recycling method for aluminum alloys. In the recycled Al-Mg-Si-based alloy, the coarse α-Al dendrites, the long plate-like β-Al5FeSi phase and bulk Mg2Si phase significantly impair the microstructure and mechanical properties of the alloys. In this works, combined the continuous rheological extrusion (CRE) technology with the addition of CRE Al-5.0Ti-1.0B (wt%) refiner, the recycled Al-Mg-Si-based alloy wires at extrusion ratios (ER) of 3, 5 and 7 were prepared. The refinement of Mg2Si and β-Al5FeSi phases and the grain refinement caused by the continuous dynamic recrystallization (CDRX) behavior in the CRE process were discussed. The strengthening mechanism of recycled Al-Mg-Si-based alloy was revealed. The results showed that, CRE technology and CRE Al-5.0Ti-1.0B (wt%) refiner can effectively refine Mg2Si and β-Al5FeSi phases, and even to the nanometer level. At the same time, the increase of ER and the addition of CRE Al-5.0Ti-1.0B (wt%) can promote the transformation of low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs), thereby promoting the occurrence of CDRX. In addition, the increase of dislocations and nanophases caused by the increase of ER and the addition of CRE Al-5.0Ti-1.0B can effectively refine CDRX grains. When 0.2 wt% CRE Al-5.0Ti-1.0B (wt%) refiner was added at ER of 7, the ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of recycled Al-Mg-Si-based alloy were 259.40 MPa, 140.80 MPa and 18.20%, respectively. Grain boundary strengthening and dislocation strengthening were the primary mechanisms in enhancing the YS of the recycled Al-Mg-Si-based alloy.

Friction stir processing on a strontium modified, thin-wall, vacuum-assisted high-pressure die-cast Aural-5 alloy to improve tensile and fatigue performance

This study explores the application of friction stir processing (FSP) to enhance the material properties of Sr-modified Aural-5 alloy, with a focus on improved tensile and fatigue properties. Aural-5 is a well-known vacuum-assisted high-pressure die-cast (HPDC) Al–Si7–Mg alloy used in the automotive industry to reduce vehicle weight, enhance fuel efficiency, and lower carbon emissions. This alloy modifies its material chemistry with Sr for fine fibrous networks of eutectic silicon and manganese (Mn) to reduce die soldering. It has significantly less iron (Fe) content resulting in the elimination of detrimental needle-shaped Fe-bearing β-phase intermetallic and improving ductility. The initial microstructure of as-received HPDC Aural-5 exhibits shrinkage porosity in the middle section, a dendritic microstructure with fibrous Al–Si eutectic colonies, a shear-band structure beneath the die-wall, large dendritic externally solidified crystals (ESCs), needle-shaped Mg2Si phase and significant second-phase particulates. Some of those microstructural features, such as porosity, ESCs, needle-shaped Mg2Si phase, and large second-phase particles, serve as initiation sites for cracks under mechanical loading, resulting in adverse effects on tensile properties, particularly ductility. FSP effectively transforms the microstructure into a wrought configuration with uniform particle distribution by eliminating porosity and disintegrating dendrites, eutectic colonies, ESCs, second-phase particles, and shear-band structures. FSP-driven microstructure modification enhances yield strength and tensile ductility by ∼30 % and ∼35 %, respectively. The fatigue life of the material in a bending mode configuration (stress ratio R = 0.1) after FSP exhibits enhancements ranging from 2.0 to 3.9 times that of the original HPDC Aural-5 alloy, depending on the applied stress level.

Experimental and theoretical investigation on refining mechanism of Mg2Si by Y addition in the Mg-Al-Si alloys

Aiming at development of new lightweight and high-strength magnesium alloys, a combined experimental and theoretical study on refining mechanism of Mg2Si by Y addition in the Mg-Al-Si alloys was performed. Two alloys, Mg63.32Al22.83Si13.85 and Mg62.56Al22.55Si14.36Y0.52 (wt.%), were prepared and investigated by combining experimental characterization with quantum-mechanical and CALPHAD calculations. The experimental results indicated that Y can refine the Mg2Si phase in Mg-Al-Si alloys but it is rather sensitive to the preparation procedure of the alloys. It was observed that Al4MgY is surrounded by Mg2Si in the as-cast alloys with Y, but it undergoes separation after homogenization annealing. First-principles calculations revealed that the mechanism of Y refining the Mg2Si phase is direct adsorption on the Mg2Si surface rather than indirect adsorption in the form of the elements atomic substitution or entering the center interstitial sites of Mg2Si. The significant refinement of the Mg2Si phase after annealing is attributed to recrystallization within the grains, eliminating the original grain boundaries, and the surface activity is reduced with Y adsorption, resulting in the formation of new and smaller Mg2Si phases. The mechanism behind the Al4MgY phase being surrounded by Mg2Si in the as-cast state but subsequent separation after homogenization annealing is not heterogeneous nucleation, but maybe due to liquid entrapment.

Microstructure evolution during solidification in a low superheat casting process of the Al-Mg2Si composites having excess Si: A phase field study

A two-dimensional phase field (PF) model of solidification during low superheat casting has been developed to grab insight into the microstructure formation mechanism of the Al-xMg2Si-ySi composite, having extra Si as the grain refining agent. The developed PF model employs a seed undercooling based nucleation model to simulate the formation of primary Mg2Si and α-Al grains, wherein the interfacial energy of the Al-melt interface is taken from literature, and a Molecular Dynamics (MD) model is employed to calculate the interfacial energy of the Mg2Si-melt interface. The simulation study predicts the microstructural parameters such as grain size, and sphericity of the primary Al and primary Mg2Si phases, as well identifies the appropriate numerical parameters such as mobility, anisotropy parameters to study the microstructure evolution in the Al-xMg2Si-ySi composites. The kinetics of grain growth of both α-Al and primary Mg2Si have been studied. Novelty of the study lies in developing a near-accurate PF model capable of optimising the weight fraction of Mg2Si and excess Si in the low superheat cast Al-xMg2Si-ySi composite system, in view of obtaining the lower grain size and higher sphericity of both primary Al and primary Mg2Si grains, which is in line with the experimental observations. The proposed PF model is capable of predicting the faceted growth of Mg2Si particles in the Al-xMg2Si-ySi composite, in presence of extra Si and during low superheat casting, and the dendritic growth of Mg2Si in the binary Al-Mg2Si composite having high Mg2Si weight fraction. Following the Jackson’s model of interface growth, it has been demonstrated that the modification of kinetic coefficient leads to a transformation of morphology of Mg2Si particles from large dendritic to faceted ones.

PEMBUATAN PADUAN INTERMETALIK Mg2Si DENGAN DOPING BISMUTH SEBAGAI MATERIAL TERMOELEKTRIK

Increasing efficiency in gasoline fuel consumption in motorized vehicles is currently continuing. One way this is done is by making use of the energy that is lost during the combustion of a motorcycle engine. About half of the energy produced during burning will be lost due to heat energy and exhaust gases. This waste heat can be utilized by converting it into another form of energy. Thermoelectric materials are those that can convert heat energy into electricity directly. Thus, in this work, we synthesized the bismuth-doped Mg2Si thermoelectric material using a solid-state reaction method using a powder in a sealed tube technique. The initial step in the production process involves measuring the raw materials bismuth, silicon, and magnesium using the Mg2Si1-xBix formula (x = 0.00, 0.025, and 0.045). The raw material powder is grinded in a shaker mill before being sealed in a stainless steel tube. The powder is sealed in a tube and heated to 800 °C for 6 hours. According to XRD test results, the Mg2Si phase and Si and MgO phases have formed. The lattice constant of the cubic Mg2Si phase was found at ~0.636 nm. A SEM investigations of surface morphology suggest that bi-doping on Si sites influences grain size refinement. Therefore, it can be concluded that the Mg2Si intermetallic alloy production process was successfully completed.

Material extrusion of high-density SiCp/7075Al composite via a high nitrogen-flowing assisted sintering

Material extrusion additive manufacturing of particle-reinforced metal matrix composite (MMC) attracts attention due to the features of uniformly sintered microstructure, easy-to-handle and low cost. However, 3D Al-MMC suffers from poor sinterability due to the stable alumina layer on alloy powder, and difficulty in removing of binders at low temperature. Here, we propose a high nitrogen-flow sintering approach for the thermal debinding and sintering of as-printed SiC particle-reinforced 7075Al (SiCp/7075Al) MMC, without using cumbersome high-vacuum system or pressure-assisted densification. Microcrystalline wax-based granular feedstock was developed based on contact angle testing experiment, which shows typical shear-thinning behavior and satisfactory printing performance. Roles of printing parameters and nitrogen flow rate in the microstructure, phases and mechanical properties of SiCp/7075Al MMC are investigated. Nitrogen flow rate of 2–2.5 L/min accelerates the breaking of oxide film, with the precipitation of intergranular MgAl2O4, Mg2Si phases, and intragranular Al2Cu phases. 3D SiCp/7075Al MMC with a high relative density of 97% and tensile strength of 308 MPa after heat treatment (HT) was achieved based on optimized printing parameters. The availability of high dense structure, combined with controlled microstructure, low-energy demand and low cost, provides a facile route for the application of 3D Al-MMC by material extrusion.

Microstructure Evolution and Mechanical Properties of 7A52 Aluminum Alloy Thin Sheet Repaired with Friction Stir Surfacing.

A solid-state repair technique based on surface friction welding is investigated in depth to achieve excellent mechanical properties of damaged 7A52 aluminum alloy. The results show that the yield strength and tensile strength along the repair direction are 436 MPa and 502 MPa, respectively, at a rotational speed of 1400 rpm and a travel speed of 300 mm/min, which are about 157.9% and 129.7% of those before the defects were repaired, respectively, while the elongation is 17.2% compared to the base material. Perpendicular to the repair direction, the yield strength and tensile strength are 254 MPa and 432 MPa, which are 111.4% and 129.7% of those before the defects were repaired, respectively, while the elongation is 11.8% compared to the base material. The mechanical properties of the repaired areas are still improved compared to those of the defect-free sheets. On the one hand, this is attributed to the dynamic recrystallization of the nugget zone due to the thermo-mechanical coupling, resulting in the formation of a fine, equiaxed grain structure; on the other hand, the precipitated Mg2Si phase, which is incoherent within the base material, transforms into the Al12(Fe, Mn)3Si phase, as well as the precipitation of the Al6Mn phase and η' phase, resulting in the enhancement of the properties. The material fracture at the junction of the nugget zone and the heat-affected zone occurs after repair, which is attributed to the significant difference in the texture of the nugget zone and the heat-affected zone, as well as to the stress concentration at the junction.

Microstructure Evolution and Strengthening Mechanism of Dual-Phase Mg-8.3Li-3.1Al-1.09Si Alloys during Warm Rolling.

In this study, the rolling process of the warm-rolled duplex-phase Mg-8.3Li-3.1Al-1.09Si alloy and the strengthening mechanism of as-rolled Mg-Li alloy were investigated. The highest ultimate tensile strength (UTS, 323.66 ± 19.89 MPa) could be obtained using a three-pass rolling process with a 30% thickness reduction for each pass at 553 K. The strength of the as-rolled LAS831 alloy is determined by a combination of second-phase strengthening, grain refinement strengthening, dislocation strengthening, and load-transfer reinforcement. Of these factors, dislocation strengthening, which is caused by strain hardening of the α-Mg phase, can produce a good strengthening effect but also cause a decrease in plasticity. The Mg2Si phase is broken up into particles or strips during the rolling process. After three passes, the AlLi particles were transformed into an AlLi phase, and the Mg2Si particles and nanosized AlLi particles strengthened the second phase to form a hard phase. The average size of the DRXed β-Li grains decreased with each successive rolling pass, and the average size of recrystallized grains in the three-pass-rolled LAS831 alloy became as low as 0.27 μm. The interface between the strip-like Mg2Si phase and the α-Mg phase is characterized by semicoherent bonding, which can promote the transfer of tensile and shear forces from the matrix to the strip-like Mg2Si phase, thereby improving the strength of the matrix and thus strengthening the LAS831 alloy.