Failure Elongation Research Articles

Role of extrusion rate on the microstructure and tensile properties evolution of ultrahigh-strength low-alloy Mg-1.0Al-1.0Ca-0.4Mn (wt.%) alloy

Mg-1.0Al-1.0Ca-0.4Mn (AXM1104, wt.%) low alloy was extruded at 200 °C with an extrusion ratio of 25 and different ram speeds from 1.0 to 7.0 mm/s. The influence of extrusion rate on microstructure and mechanical properties of the AXM1104 alloy was systematically studied. With the increasing of extrusion rate, the mean dynamically recrystallized (DRXed) grain size of the low alloy and average particles diameter of precipitate second phases were increased, while the degree of grain boundary segregation and the intensity of the basal fiber texture were decreased. With the rising of extrusion rate from 1.0 to 7.0 mm/s, the tensile yield strength (TYS) of the as-extruded AXM1104 alloy was decreased from 445 MPa to 249 MPa, while the elongation to failure (EL) was increased from 5.0% to 17.6%. The TYS, ultimate tensile strength (UTS) and EL of the AXM1104 alloy extruded at the ram speed of 1.5 mm/s was 412 MPa, 419 MPa and 12.0%, respectively, exhibiting comprehensive tensile mechanical properties with ultra-high strength and excellent plasticity. The ultra-high TYS of 412 MPa was mainly due to the strengthening from ultra-fine DRXed grains with segregation of solute atoms at grain boundaries. The strain hardening rate is increase slightly with increasing extrusion speed, which may be ascribed to the increasing mean DRXed grain size with rising extrusion speed. The higher strain hardening rate contributes to the higher EL of these AXM1104 samples extruded at higher ram speed.

High-ductility fine-grained Mg-1.92Zn-0.34Y alloy fabricated by semisolid and then hot extrusion

The combination of semisolid and hot extrusion processing was applied to refine the icosahedral quasicrystalline phase (I-phase) in an extruded Mg-1.92Zn-0.34Y(wt.%) alloy for the first time. The semisolid isothermal heat treatment transformed the micron-sized I-phase particles into nano lamellar eutectic (α-Mg + I-phase) with a lamellar spacing of ~86 nm. After subsequent hot extrusion at 250 °C, the nano lamellar eutectic phases were broken into uniformly dispersed nanoscale I-phase particles. What's more, the matrix microstructure was significantly refined with an equiaxed average grain size of 2.59 ± 0.81 µm, and an unusual texture component (most of the grains’ c-axis is parallel to the extrusion direction) was observed. The processed alloy exhibited a high tensile elongation to failure (EL) of 44 ± 2.6% with an ultimate tensile strength (UTS) of 258 ± 2.0 MPa and a tensile yield strength (TYS) of 176 ± 1.6 MPa at room temperature. The high ductility from the combined effects of the grain refinement, dispersion of nanoscale I-phase particles, and the unusual texture. The uniform dispersion of nanoscale I-phase particles could promote grain refinement by particle stimulated nucleation mechanism, and thus bring the unusual texture (where the c-axis is aligned parallel to the extrusion direction during dynamic recrystallization, which contributed to ductility).

Effects of pre-aging on microstructure evolution and deformation mechanisms of hot extruded Mg–6Zn–1Gd–1Er Mg alloys

Abstract The influence of pre-aging treatment on the microstructure, texture and mechanical properties of the Mg–6Zn–1Gd–1Er (wt.%) alloy was investigated. The microstructure analysis shows that the presence of pre-aging is beneficial to { 10 1 ¯ 2 } twin nucleation at the early stage of extrusion and inhibits the growth of twins and promotes the formation of [ 10 1 ¯ 0 ] -fiber texture components, thus accelerating the complex process of recrystallization. In the middle stage of extrusion, the extruded samples under the condition of solid solution were subjected to dynamic precipitation during severe shear deformation. The precipitation of the second phase particles followed the particle stimulating nucleation (PSN) mechanism, which increased the volume fraction of DRX grains during extrusion. In the extruded samples under the peak-aged condition, the particles appear dissolved during the severe shear deformation strain, which slows down the DRX process. In the later stage of extrusion, the small rod-shaped particles followed the PSN mechanism, and finally formed the strong fiber texture. The extruded alloy exhibits the strongest mechanical properties under the peak-aged state, with ultimate tensile strength (UTS) of 346 MPa, tensile yield strength (TYS) of 217 MPa, and elongation to failure (EL) of 13.6%. The improvement of mechanical properties is mainly attributed to the existence of strong fiber texture, small rod-shaped and block-shaped phases.

An investigation of microstructure and mechanical properties of as-cast Zn–22Al alloy during homogenizing and equal channel angular pressing

In this study, the effect of homogenization heat treatment and equal channel angular pressing process (ECAP) on microstructure and mechanical properties were explored in Zn–22Al alloy. It was observed that homogenization caused a significant part of the structure to transform to equiaxed grains from an initially lamellar structure. Also, with increasing time of homogenization, a homogeneous structure with no coarse phases were created. Average grain sizes of 48, 2.5, 1.2 and 1.1 μm were respectively achieved after homogenization for 4, 8, 12 and 24 h at 375 °C followed by water quenching. By removal of the lamellar structure during homogenization, improved superplastic behavior was observed. By increasing the time of homogenization, a decrease in microhardness took place which can be due to the loss of hard dendritic phases in the microstructure. On the other hand, grain size of 0.44 μm was achieved after 8 passes of ambient temperature ECAP process which was found to be quite effective in forming the ultra-fine grained (UFG) and equiaxed microstructure leading to further improvement in superplastic behavior. By increasing the number of ECAP passes, the failure elongation increased. On the other hand, the microhardness curve showed a work softening which is associated with the dynamic recovery/recrystallization of η phase after ECAP process.

Ductility enhancement by activating non-basal slip in as-extruded Mg alloys with dilute Sc addition

This work systematically investigates the impact of the dilute Sc addition on microstructures and mechanical properties in Mg alloys. Electron back scattered diffraction, slip traces analysis, transmission electron microscopy, and visco-plastic self-consistent polycrystal constitutive (VPSC) modeling were performed to investigate the deformation mechanisms in the tensile testing, especially the activation of <c+a> slip. The results showed that as-solid solution samples only consisted of α-Mg phase. After extrusion, all samples exhibited a similar average grain size. With the increment of the Sc content, the ductility of the samples was significantly improved, which failure elongation (FL) of Mg-xSc (x = 0.3, 0.6, 0.9 wt.%) alloys improved from 14.4% to 24.8%. The yield strength of each alloy is similar, about 200 MPa. VPSC results indicated that the difference value of the initial slip resistance (τ0) between prismatic slip and basal slip decreases from 63 MPa to 49 MPa, and the difference value of τ0 between pyramidal slip and basal slip decreases from 72 MPa to 57 MPa. The VPSC and the two-beam diffraction results confirmed that the pyramidal <c+a> slip and prismatic <a> slip were activated in tensile testing. The quantitative analysis of the slip trace line verified that the volume of non-basal slip reached 49.5% when the Sc content increased to 0.9 wt.%. Therefore, the addition of Sc in solid solution increased the amount of pyramidal <c+a> and prismatic <a> dislocation activities during the deformation process, which was beneficial to coordinate the c-axis strain, and finally improved ductility of Mg alloy.

Effect of Water-Induced and Physical Aging on Mechanical Properties of 3D Printed Elastomeric Polyurethane.

In this study, the effect of moisture on the elastic and failure properties of elastomeric polyurethane (EPU 40) 3D printed via Vat Photopolymerization was investigated. EPU 40 samples were printed, and uniaxial tensile tests were performed on Dry-fresh, Dry-aged (eight months aged), and after various times of being immersed in water (0-8 months). Elastic response, initial stiffness, failure strength, and failure elongation were analyzed. Besides, gravimetric analysis was performed to determine the increase in weight and thickness after water immersion. The elastic response was fitted by the Arruda-Boyce constitutive model. Results show that initial stiffness decreased after immersion (mean 6.8 MPa dry vs. 6.3 MPa immersed p-value 0.002). Contrary, the initial stiffness increased due to physical aging under a dry state from a mean 6.3 MPa to 6.9 MPa (p = 0.006). The same effect was observed for stiffness parameter G of the constitutive model, while the limit stretch parameter λL was not affected by either aging. The 95% confidence intervals for strength and failure stretch were 5.27-9.48 MPa and 2.18-2.86, respectively, and were not affected either by immersion time or by physical aging. The median diffusion coefficient was 3.8·10-12&amp;nbsp;m^2/s. The immersion time has a significant effect only on stiffness, while oxidative aging has an inverse effect on the mechanical properties compared to water immersion. The transition process is completed within 24 h after immersion.

Tailoring phase composition of a multielement TiZrAlV alloy via electroplastic rolling

• Effect of strain on electroplastic deformed ZrTiAlV alloy was studied. • Martensitic transformation of Ti alloy can be regulated by electroplastic rolling. • Increasing strain enhances the stress-induced martensite transformation and improves the strength. • The optimal mechanical properties of UTS ∼1398 MPa and ε f ∼ 5.77% were obtained at strain 2.28. The TiZrAlV alloy were deformed by electroplastic rolling with strains from e ∼ 1.31 to 2.70, which led to the phase transformation from β phase to α phase and α phase to α˝ phase. The contents of various phases were tailored by rolling strain. As a result, the deformed alloy exhibited an increasing ultimate tensile strength (1286 MPa to 1398 MPa) and failure elongation (4.05% to 5.77%) from e ∼ 1.31 to 2.28. Further increasing the strain to e ∼ 2.70 led to a further increase in strength and a loss in ductility, 1484 MPa and 3.73%. Our work provides an alternative process to improve the mechanical properties of Ti alloys by tailoring various phase compositions and phase transformations.

Fabrication, microstructure characterization and mechanical properties of B4C microparticles and SiC nanowires hybrid reinforced aluminum matrix composites

Due to the high modulus, high strength, low density, excellent wear resistance and good neutron absorption, the boron carbide (B 4 C) particle reinforced aluminum (Al) matrix composites have been widely applied in the aerospace, weaponry, transportation and neutron shielding fields. In response to the increasing requirement of better strength -ductility matching of B 4 C/Al composites, introducing a nano-scale reinforcement into the B 4 C/Al composites becomes an attractive research focus. In this work, the SiC nanowires were ball-milled with Al powders, and then the SiC/Al composite powders were mixed with B 4 C microparticles. Thus, the 15vol. % B 4 C/SiC/Al composites with different volume fractions of SiC nanowires were fabricated by hot-pressing sintering and hot extrusion. B 4 C microparticles and SiC nanowires are uniformly dispersed in the B 4 C/SiC/Al composites, while the introduced SiC nanowires effectively decrease the Al matrix grain sizes. B 4 C/SiC/Al composites produce the better strength-ductility matching than that of B 4 C/Al composites, while the 15vol. % B 4 C/SiC/Al composite with 1vol. % SiC nanowires achieved the best strength-ductility matching. It generates the 281.7 ± 2.7 MPa in yield strength, 351.2 ± 0.1 MPa in ultimate tensile strength and 5.9 ± 0.7% in failure elongation, which are increased by 18.2%, 15.1% and 13.5% compared to the B 4 C/Al composites. Uniformly dispersed B 4 C microparticles and SiC nanowires largely block the dislocation motions and improve the dislocation storage capacity, which results in a more significant hetero-deformation induced (HDI) hardening effect in the B 4 C/SiC/Al composites. Moreover, the B 4 C/Al interfacial transition regions with the added SiC nanowires becomes stronger, which can enhance the load transfer efficiency of the B 4 C/Al interfaces as a result of the existing dislocation hardening zones. In conclusion, it is a good strategy to combine the synergistic strengthening effect of micro-scale and nano-scale reinforcements in the metal matrix composites. • The hybrid reinforcements of B 4 C microparticles and SiC nanowires generate a synergistic strengthening effect on the mechanical properties of B 4 C/SiC/Al composites. • The yield strength, ultimate tensile strength and failure elongation of B 4 C/SiC/Al composites with 1vol. % SiC nanowires are increased by 18.2%, 15.1% and 13.5% respectively compared to those of the B 4 C/Al composites. • SiC nanowires increase the geometrically necessary dislocations densities in the B 4 C/SiC/Al composites, which contribute to the heteto-deformation induced hardening effect and load transfer efficiency of the B 4 C/Al interface.

Ultra strength-ductility synergy in the Mg-Al-Zn alloy via densely dispersed multi-scale {10[formula omitted]} tension twins

Enhancing the strength and ductility of widely used Mg–Al–Zn alloys is an urgent requirement for Mg alloy load-bearing components. Ultra-fine grains and a large amount of β-Mg17Al12 precipitates improve their strength but reduce ductility. This work developed a commercial AZ80 alloy with the ultimate tensile strength (UTS) of 512 MPa and elongation to failure (EF) of 19.8% using a combination of extrusion and multi-directional forging processes, which has superior strength-ductility synergy among the reported AZ80 alloys and reaches the level of wrought Mg-RE alloys. The excellent mechanical properties are attributed to the formation of densely dispersed multi-scale {1012‾} tension twins. The introduction of ultra-fine {1012‾} twins reduces the mean free path of dislocations leading to a faster dislocation accumulation, which improves the work hardening ability of the alloy. This work provides a new insight into the development of low-cost Mg alloy forging billets with high strength and ductility.

Laser powder bed fusion of Al–Mg–Zr alloy: Microstructure, mechanical properties and dynamic precipitation

A Sc-free and high-plasticity Al-4.8Mg-1.6Zr aluminum alloy was densified via laser powder bed fusion. The microstructure features a typical bimodal grain structure, with abundant L12-Al3Zr particles about 100 nm distributed. The yield strength (YS) of 449 ± 4 MPa, ultimate tensile strength (UTS) of 449 ± 5 MPa, and the elongation to failure (EL) of 15.1 ± 1.9% are obtained after peak aging. In addition to solid solution strengthening, grain boundary strengthening and nanoparticle strengthening, the long-range stacked ordered 9R phase associated with high content Mg and Zr also contributes to strengthening. Besides, the difference in strain distribution between coarse and fine grain zones causes deformation-induced hardening. Low-temperature dynamic precipitation is observed in this Al–Mg–Zr alloy for the first time. The deformation-induced hardening and dynamic precipitation improve the strain-hardening capability, consequently delaying necking instability. After peak aging treatment, the number of Al3Zr particles with strong high-temperature stability increases, inhibiting grain coarsening and enhancing the precipitation strengthening effect. The excellent strength-ductility trade-off of the printed Al–Mg–Zr without expensive Sc element gives it a broad application prospect in economical and large-scale additive manufacturing.

Microstructure evolution and mechanical properties of industrial scale samples of Mg–Gd–Y–Zn–Zr alloy after repetitive upsetting-extrusion process

As one of the severe plastic deformation (SPD) methods, repetitive upsetting-extrusion (RUE) technique was an effective way to refine grains for large-sized billet at blank-making stage. The microstructure evolution and mechanical properties of industrial-scale Mg–9Gd–3Y–2Zn–0.4Zr (wt.%) alloys were comprehensively investigated in this paper. The experimental alloys exhibited heterogeneous microstructure in the different regions and directions due to the uneven deformation temperature and strain during the RUE deformation process. In addition, the texture and mechanical properties of the RUEed samples also exhibited obvious anisotropy. In particular, the RUEed sample in the edge region along extrusion direction (EED) showed a superior tensile strength with ultimate tensile strength (UTS) of 357 MPa, tensile yield strength (TYS) of 242 MPa and the failure elongation (FE) of 9.0%, due to the smaller average grain size (12.7 μm) and higher area fraction of the dynamic recrystallized (DRXed) grains (82.2%) than other regions. Furthermore, the results also exhibited that the enhancement of the mechanical properties of the RUEed samples were mainly attributed to Hall–Petch strengthening, Orowan strengthening and texture strengthening.

A rolled Mg−8Al−0.5Zn−0.8Ce alloy with high strength-ductility synergy via engineering high-density low angle boundaries

Developing low-cost rolled Mg alloys with both high strength and ductility is desirable, while the improved strength is generally accompanied with decreased ductility. Here, by using rotated hard-plate rolling (RHPR) with a total thickness reduction of ∼85%, we obtained a Mg−8Al−0.5Zn−0.8Ce (wt.%, AZ80−0.8Ce) alloy with a high strength-ductility synergy, i.e., the yield strength (YS), ultimate tensile strength (UTS) and elongation-to-failure (EF) are ∼308 MPa, ∼360 MPa and ∼13.8%, respectively. It reveals that the high YS is mainly originated from grain boundary strengthening (∼212 MPa), followed by dislocation strengthening (∼43 MPa) and precipitation hardening (∼25 MPa). It is found that a relatively homogeneous fine grain structure containing a large fraction (∼62%) of low angle boundaries (LABs) is achieved in the RHPRed alloy, which is benefit for the high tensile EF value. It demonstrates that LABs have important contributions to strengthening and homogenizing tensile deformation process, leading to the simultaneous high strength and high EF. Our work provides a new insight for fabrication of low-cost high performance Mg alloys with an excellent strength-ductility synergy.

Effect of Direct Recycling Hot Press Forging Parameters on Mechanical Properties and Surface Integrity of AA7075 Aluminum Alloys

The current practice in aluminum recycling plants is to change the waste into molten metal through the conventional recycling (CR) manufacturing process. However, the CR technique is so energy-intensive that it also poses an indirect threat to the environment. This paper presents a study on meltless direct recycling hot press forging (DR-HPF) as an alternative sustainable approach that has fewer steps with low energy consumption, as well as preventing the generation of new waste. A laboratory experiment was conducted to study the mechanical properties and surface integrity of AA7075 aluminum alloy by employing a hot press forging (HPF) process under different temperatures (380, 430, and 480 °C) and holding times (0, 60, and 120 min). It was found that as the parameter increased, there was a positive increase in ultimate tensile strength (UTS), elongation to failure (ETF), density, and microhardness. The recycled chips exhibit the best mechanical properties at the highest parameters (480 °C and 120 min), whereas the UTS = 245.62 MPa and ETF = 6.91%, while surface integrity shows that the calculated microhardness and density are 69.02 HV and 2.795 g/cm3, respectively. The UTS result shows that the highest parameters of 480 °C and 120 min are comparable with the Aerospace Specification Metals (ASM) Aluminum AA7075-O standard. This study is a guide for machinists and the manufacturing industry to increase industry sustainability, to preserve the earth for future generations.

A study on the mechanical and electrical properties of high-strength CuCrZr alloy fabricated using laser powder bed fusion

Copper-chromium-zirconium (CuCrZr) is tailored using additive manufacturing, particularly laser powder bed fusion (LPBF). Due to high thermal conductivities and high reflectivity of infrared laser irradiation, it is still challenging to fabricate copper alloys using the LPBF technique. To address the issue, a short wavelength laser (515 nm) was employed in the LPBF process. In this work, the CuCrZr alloys were built with optimized building parameters such as powder of 485 W, scanning speed of 400 mm/s, and hatching distance of 0.09 mm. The relative density of the samples was found to be 98.07 %. The as-built samples exhibit good mechanical properties with ultimate tensile strength (UTS) of 447 ± 13 MPa, yield strength (YS) of 400 ± 11 MPa, total failure elongation (EL) of 10 ± 3 %, and Vickers hardness of 130 ± 15 HV). However, the electrical property is poor with 30 ± 1 %IACS. The high tensile stress and low electrical conductivity may attribute to the dislocation cells. Moreover, the dissolved Cr atoms result in poor conductivity. By direct aging treatment at 500 °C for 1 h, excellent mechanical properties (UTS = 566 ± 18 MPa, YS = 487 ± 13 MPa, EL = 15 ± 1 %, Vickers hardness = 161 ± 15 HV) were achieved while maintaining a good conductivity (64 ± 3 % IACS). The main contribution to the increase in YS is attributed to (I) the nanoscale Cr precipitated homogeneously in the copper matrix during the direct aging treatment and (II) the remaining high dislocation density near the dislocation cells. The enhancement of the electrical conductivity is attributed to the decomposition of the supersaturated solid solution.

Extraordinary ductility enhancement of Mg-Nd-Zn-Zr alloy achieved by electropulsing treatment

Mg-Nd-Zn-Zr (JDBM) alloy was studied as a candidate for biodegradable implant material because of its moderate mechanical properties, good biocompatibility, and favorable uniform degradation behavior. To verify whether JDBM alloy exhibits electroplasticity effect and then study the mechanism of electropulsing treatment on JDBM alloy, in this study, homogenized and pre-tensile deformed samples were treated by electropulsing. After the electropulsing treatment, the average grain size was refined due to recrystallization, micron-scale Mg12Nd secondary phases precipitated slightly, while the morphology of nanoscale Zr particles changed from rodlike to ellipsoidal shape. The elongation to failure (EL) increased obviously for the homogenized and pre-tensile deformed JDBM alloy samples after electropulsing treatment, accompanying with no obvious sacrifice of the yield strength (YS) for the former and an evident decrease of YS for the latter, mainly due to the reduction of the dislocation density. The YS decrement and EL increment (77.57%) for the latter are more apparent attributed to the higher density of dislocations introduced by pre-tensile deformation. Therefore, the electropulsing treatment can obviously improve the mechanical properties of JDBM alloy, especially for the plasticity. The present work opens a new window for the fabrication of JDBM alloy profiles with high mechanical properties, especially for the plasticity, such as the cold drawing wires and tubes for biomedical applications. It also could provide theoretical references for other magnesium alloy processing.

Effect of annealing temperature on tensile fracture behavior of AZ31/6061 explosive composite plate

In this study, the first evaluated and analyzed the local strain evolution and macro fracture morphology of AZ31/6061 explosive composite plate during uniaxial tension by the digital image correlation (DIC) method. The materials used are double-layer AZ31/6061 composite plates prepared by the explosive welding process. In order to meet the subsequent forming requirements, annealing at different temperatures is carried out. The fracture damage mechanism of AZ31/6061 explosive clad plate was comprehensively studied through mechanical tests at different annealing temperatures, microstructure characterization and fracture behavior analysis during the tensile process. The results showed that the thickness of the intermetallic compound at the interface increased with the increase of temperature, and the interface bonding strength reached the highest at 150 °C. Under the condition of 200 °C/2 h annealing, the composite plate has the best comprehensive properties, the tensile strength is 253.51 MPa, and the failure elongation is 25.16%. Combined with the SEM observation of tensile fracture and the evolution of strain distribution measured by digital image correlation (DIC), it is shown that the composite plate is mainly a brittle fracture mechanism before annealing and a ductile-brittle mixed fracture mechanism after annealing. Revealed the effect of temperature on the interfacial strengthening mechanism and fracture behavior of Mg/Al composite plate during fracture.

Effect of micro-alloyed Ce on the microstructure evolution and mechanical properties of rolled Mg–0.6Al–0.5Mn–0.2Ca alloy sheets

In this study, the effect of minor Ce addition (0, 0.1, and, 0.3 wt.%) on the microstructure evolution and mechanical properties of rolled Mg–0.6Al–0.5Mn–0.2Ca (AMX100) alloy sheets is systematically investigated under different annealing processes. With 0.1 wt.% Ce addition, partial Al8Mn5 phases turn into Al8Mn4Ce. With 0.3 wt.% Ce addition, the number of the Al8Mn4Ce further increases and the Al–Ce phases are observed. The single-stage annealed alloys exhibit similar uniform fine-grained structures (∼6 μm) regardless of the Ce content, while the grain sizes of the two-stage annealed alloys increase obviously (∼10.9–11.9 μm). Especially, the abnormal grain growth occurs in the two-stage annealed AMX100-0.3Ce alloy. After the aging treatment, the yield strength (YS) of the two-stage annealed alloys is increased by ∼25–45 MPa, which is greatly higher than that of the single-stage annealed alloys (∼1–8 MPa). Note that the two-stage annealed AMX100–0.1Ce alloy displays a significant age-hardening response with the ultimate tensile strength (UTS) of ∼272 MPa and the elongation to failure (EF) of ∼14%, which is attributed to the formation of Al and Ca enriched Guinier-Preston (G.P.) zones. This work sheds light on the design and fabrication of low-cost dilute magnesium alloys with admirable age-hardening ability.

Risks Associated with the Use of Hydrogen as an Energy Carrier or Source

Hydrogen is a dangerous gas due to its low ignition energy, wide flammability range, promotion of the embrittlement of steel, and its high coefficient of permeation for polymers. The fracture toughness and failure elongation of pipe steels are strongly impacted by hydrogen embrittlement, whereas yield stress and ultimate strength are moderately impacted. Specific tools are required for the pipe defect assessment used for the transport of hydrogen, which is pure or blended with natural gas. The safety factors associated with cracks or scratches are obtained through the failure assessment diagram or the notch failure assessment diagram. The corrosion defects are assessed by limit analysis, and the estimated repair factor and dents are evaluated by computing the damage value under service pressure. The design factor in the calculation of the maximum admissible operating pressure (MAOP) is modified depending on the location of the pipes to account for the lethal risks from the torch effect or explosion. It is crucial to monitor the leaks due to hydrogen permeation through domestic hydrogen distribution networks, particularly in closed areas.

Influence of grain size on microstructure, mechanical properties and strain hardening behavior of Mg-0.3Ca (wt.%) alloy

Mg-0.3Ca (X03, wt.%) binary alloy with different grain sizes were obtained by low-temperature extrusion and subsequent annealing heat treatment. The tensile yield strength (TYS), ultimate tensile strength (UTS) and elongation to failure (EL) of the as-extruded X03 binary alloy with an ultra-fine grain size of 0.7 μm was 361 MPa, 370 MPa and 10.6%, respectively. The exceptional high TYS of 361 MPa was mainly due to the strengthening from ultra-fine dynamic recrystallized grains with segregation of Ca atoms at grain boundaries. The high energy barrier for dislocation emission from grain boundaries pinned by segregated Ca atoms increases the tensile stress required to activate dislocation nucleation. With increasing average grain sizes from 0.7 μm to 6.0 μm after annealing treatment, the TYS of the X03 alloy was decreased obviously from 361 MPa to 94 MPa, while the EL increases from 10.6% to 29.6%. Abnormal strain softening was observed during tensile test of the fine-grained samples with grain size less than 2 μm. The mechanism of strain softening may be mainly caused by the decrease of <a> type dislocations density. The alloy with average grain size larger than 2 μm attains more space to store dislocations, thus shows obvious strain hardening, which contributes to high elongation to failure.

Impact of Chromium Addition on the UTS and ETF of Aluminium Alloy AA6061 Chips Based Composite

Aluminium matrix composite has been increasingly developed due to the impressive performances demonstrated, mechanically and physically. The related properties were enhanced with the addition of reinforcing materials and this tailor-made composite can be used in the area of automotive, aerospace and military. In this study, the matrix composite was developed directly from aluminium chips without remelting through a series of hot press forging operations. This process involved heating the aluminium chip mixtures with 1 to 8 wt% chromium content above the recrystallization temperature. Then, the uniaxial force was subsequently applied onto the composite. For performance measures, the hot pressed composites were tested for the ultimate tensile strength (UTS) and elongation to failure (ETF). The composite with 2 wt % of chromium exhibits significant improvement compared to other samples, with the UTS and ETF reached to 215.37 MPa and 30.65% respectively. This sample exceeds the minimum stress and strain of stock aluminium AA6061-T4. Furthermore, the addition of chromium beyond 2 wt % would generally cause reduction of the mechanical properties of the composite.