Effect of non-isothermal aging on microstructure and properties of Al–5.87Zn–2.07Mg–2.42Cu alloys

The evolution of microstructure and properties of Al–5.87Zn–2.07Mg–2.42Cu alloys during non-isothermal aging was studied. The mechanical properties of the alloy were tested by stretching at room temperature. The results show that in the non-isothermal aging process, when the alloy is cooled to 140 °C, the ultimate tensile strength of the alloy reaches a maximum value of 582 MPa and the elongation is 11.9%. The microstructure was tested through a transmission electron microscope, and the experimental results show that the GP zones and η’ phases are the main strengthening precipitates. At the cooling stage, when the temperature dropped to 180 °C, the GP zones were precipitated again. Besides, the experimental results show that the main strengthening phase during non-isothermal aging is η’ phases.     

Effect of Al addition on microstructure and mechanical properties of Mg−Zn−Sn−Mn alloy

The microstructure and properties of the as-cast, as-homogenized and as-extruded Mg−6Zn−4Sn−1Mn (ZTM641) alloy with various Al contents (0, 0.5, 1, 2, 3 and 4 wt.%) were investigated by OM, XRD, DSC, SEM, TEM and uniaxial tensile tests. The results show that when the Al content is not higher than 0.5%, the alloys are mainly composed of α-Mg, Mg₂Sn, Al₈Mn₅ and Mg₇Zn₃ phases_. When the Al content is higher than 0.5%, the alloys mainly consist of α-Mg, Mg₂Sn, MgZn, Mg₃₂(Al,Zn)₄₉, Al₂Mg₅Zn₂, Al₁₁Mn₄ and Al₈Mn₅ phases. A small amount of Al (≤1%) can increase the proportion of fine dynamic recrystallized (DRXed) grains during hot-extrusion process. The room- temperature tensile test results show that the ZTM641−1Al alloy has the best comprehensive mechanical properties, in which the ultimate tensile strength is 332 MPa, yield strength is 221 MPa and the elongation is 15%. Elevated- temperature tensile test results at 150 and 200 °C show that ZTM641−2Al alloy has the best comprehensive mechanical properties.     

Effect of Al addition on microstructure and mechanical properties of Mg−Gd−Zn alloys

The microstructure evolution and mechanical properties of Mg?15.3Gd?1Zn alloys with different Al contents (0, 0.4, 0.7 and 1.0 wt.%) were investigated. Microstructural analysis indicates that the addition of 0.4 wt.% Al facilitates the formation of 18R-LPSO phase (Mg₁₂Gd(Al, Zn)) in the Mg?Gd?Zn alloy. The contents of Al₁₁Gd₃ and Al₂Gd increase with the increase of Al content, while the content of (Mg, Zn)₃Gd decreases. After homogenization treatment, (Mg, Zn)₃Gd, 18R-LPSO and some Al₁₁Gd₃ phases are transformed into the high-temperature stable 14H-LPSO phases. The particulate Al?Gd phases can stimulate the nucleation of dynamic recrystallization by the particle simulated nucleation (PSN) mechanism. The tensile strength of the as-rolled alloys is improved remarkably due to the grain refinement and the fiber-like reinforcement of LPSO phase. The precipitation of the β′ phase in the peak-aged alloys can significantly improve the strength. The peak-aged alloy containing 0.4 wt.% Al achieves excellent mechanical properties and the UTS, YS and elongation are 458 MPa, 375 MPa and 6.2%, respectively.     

Effects of minor Sc and Zr additions on mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys

The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ultimate tensile strength of the peak-aged Al−Zn−Mg−Cu alloy is improved by about 105 MPa with the addition of 0.10% Zr. An increase of about 133 MPa is observed with the joint addition of 0.07% Sc and 0.07% Zr. For the alloys modified with the minor addition of Sc and Zr (0.14%), the main strengthening mechanisms of minor addition of Sc and Zr are fine-grain strengthening, sub-structure strengthening and the Orowan strengthening mechanism produced by the Al₃(Sc,Zr) and Al₃Zr dispersoids. The volume of Al₃Zr particles is less than that of Al₃(Sc,Zr) particles, but the distribution of Al₃(Sc,Zr) particles is more dispersed throughout the matrix leading to pinning the dislocations motion and restraining the recrystallization more effectively.     

Effects of Mg content on microstructure and mechanical properties of low Zn-containing Al−xMg−3Zn−1Cu cast alloys

Effects of Mg content on the microstructure and mechanical properties of low Zn-containing Al?xMg? 3Zn?1Cu cast alloys (x=3?5, wt.%) were investigated. As Mg content increased in the as-cast alloys, the grains were refined due to enhanced growth restriction, and the formation of η-Mg(AlZnCu)₂ and S-Al₂CuMg phases was inhibited while the formation of T-Mg₃₂(AlZnCu)₄₉ phase was promoted when Mg content exceeded 4 wt.%. The increase of Mg content encumbered the solution kinetics by increasing the size of eutectic phase but accelerated and enhanced the age-hardening through expediting precipitation kinetics and elevating the number density of the precipitates. As Mg content increased, the yield strength and tensile strength of the as-cast, solution-treated and peak-aged alloys were severally improved, while the elongation of the alloys decreased. The tensile strength and elongation of the peak-aged Al?5Mg?3Zn?1Cu alloy exceed 500 MPa and 5%, respectively. Precipitation strengthening implemented by T′ precipitates is the predominant strengthening mechanism in the peak-aged alloys and is enhanced by increasing Mg content.     

Effect of thermal exposure on microstructure and mechanical properties of Al−Si−Cu−Ni−Mg alloy produced by different casting technologies

The effect of thermal exposure at 350 °C for 200 h on microstructure and mechanical properties was investigated for Al−Si−Cu−Ni−Mg alloy, which was produced by permanent mold casting (PMC) and high pressure die casting (HPDC). The SEM and IPP software were used to characterize the morphology of Si phase in the studied alloys. The results show that the thermal exposure provokes spheroidization and coarsening of eutectic Si particles. The ultimate tensile strength of the HPDC alloy after thermal exposure is higher than that of the PMC alloy at room temperature. However, the TEPMC and TEHPDC alloys have similar tensile strength around 67 MPa at 350 °C. Due to the coarsening of eutectic Si, the TEPMC alloy exhibits better creep resistance than the TEHPDC alloy under studied creep conditions. Therefore, the alloys with small size of eutectic Si are not suitably used at 350 °C.     

Effect of Gd on microstructure,mechanical properties,and corrosion behavior of as-homogenized Mg−8Li−3Al−2Zn−0.2Zr alloy

The microstructure observation, tensile test, electrochemical measurement, and corrosion morphology characterization were conducted to study the effect of Gd on the microstructure, mechanical properties, and corrosion behavior of as-homogenized Mg?8Li?3Al?2Zn?0.2Zr (LAZ832?0.2Zr) alloy. The addition of trace Gd can improve the mechanical properties of as-homogenized LAZ832?0.2Zr alloy by refining the microstructure, reducing the content of AlLi softening phase, and forming Al₂Gd strengthening phase. Meanwhile, the addition of trace Gd can weaken the microgalvanic corrosion between matrix phase and AlLi phase, inhibit the galvanic corrosion between α-Mg phase and β-Li phase, and result in the formation of dense oxide film containing Gd₂O₃, thereby improving the corrosion resistance of the alloy. When the Gd content is 1.0 wt.%, the alloy shows the best comprehensive properties with the ultimate tensile strength of 189.8 MPa, elongation of 42.3%, and corrosion rate (determined by hydrogen evolution) of 0.86 mm·a^?1.     

Effect of Y addition on microstructure and mechanical properties of Mg–Zn–Mn alloy

The effects of Y on the microstructure and mechanical properties of Mg–6Zn–1Mn alloy were investigated. The results show that the addition of Y has significant effect on the phase composition, microstructure and mechanical properties of Mg–6Zn–1Mn alloy. Varied phases compositions, including Mg₇Zn₃, I-phase (Mg₃YZn₆), W-phase (Mg₃Y₂Zn₃) and X-phase (Mg₁₂YZn), are obtained by adjusting the Zn to Y mass ratio. Mn element exists as the fine Mn particles, which are well distributed in the alloy. Thermal analysis and microstructure observation reveal that the phase stability follows the trend of X>W>I>Mg₇Zn₃. In addition, Y can improve the mechanical properties of Mg–Zn–Mn alloy significantly, and the alloy with Y content of 6.09% has the best mechanical properties. The high strength is mainly due to the strengthening by the grain size refinement, dispersion strengthening by fine Mn particles, and introduction of the Mg–Zn–Y ternary phases.     

Effects of Li content on microstructure and mechanical properties of as-cast Mg−xLi−3Al−2Zn−0.5Y alloys

The effects of Li content on the microstructure and mechanical properties of the as-cast Mg?xLi?3Al?2Zn? 0.5Y (LAZx32-0.5Y) alloys were investigated by XRD, SEM, TEM, hardness tester and universal testing machine. The results show that the matrix of the alloy transforms from α-Mg to α-Mg+β-Li and then to β-Li when the Li content increases from 4% to 14% (mass fraction). All LAZx32-0.5Y alloys contain AlLi and Al₂Y, while MgLi₂Al appears only in the alloy containing the β-Li matrix. As the Li content increases, the content of AlLi and MgLi₂Al gradually increases, while the content of Al₂Y does not change much. As the Li content increases from 4% to 10%, the ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually decrease while the elongation gradually increases. The corresponding fracture mechanism changes from cleavage fracture to quasi-cleavage fracture and then to microporous aggregation fracture. This is mainly attributed to the decrease of α-Mg and the increase of β-Li in the alloy. When the Li content continues to increase to 10% and 14%, the yield strength, ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually increase, while the elongation decreases sharply, which is mainly attributed to the nano-scale MgLi₂Al uniformly distributed in the β-Li matrix.     

Effect of Cu on microstructure and mechanical properties of 2519 aluminum alloy

The effect of Cu on the microstructure and mechanical properties of 2519 aluminum alloy was investigated by means of tensile test, microhardness test, transmission electron microscopy, and scanning electron microscopy. The results show that when the content of Cu is less than 6.0%, the strength of 2519 aluminum alloy increases with the increase of Cu eontent; when the content of Cu is more than 6.0%, the strength of the alloy decreases. The hardening effect of the aged alloy is accelerated at 180℃ and the time to peak age is reduced, but the plasticity of the alloy gradually decreases with the increase of Cu content. However, the hardening effect of the aged alloy decreases with the increase of Cu as the content of Cu is over 6.0%. The optimal content of Cu of 2519 aluminum alloy is 6.0%, at which the alloy has best tensile strength and plasticity.     

Microstructure and mechanical properties of squeeze-cast Al−5.0Mg−3.0Zn−1.0Cu alloys in solution-treated and aged conditions

The microstructure and mechanical properties at different depths of squeeze-cast, solution-treated and aged Al−5.0Mg−3.0Zn−1.0Cu alloy were investigated. For squeeze-cast alloy, from casting surface to interior, the grain size of α(Al) matrix and width of T-Mg₃₂(AlZnCu)₄₉ phase increase significantly, while the volume fraction of T phase decreases. The related mechanical properties including ultimate tensile strength (UTS) and elongation decrease from 243.7 MPa and 2.3% to 217.9 MPa and 1.4%, respectively. After solution treatment at 470 °C for 36 h, T phase is dissolved into matrix, and the grain size increases so that the UTS and elongation from surface to interior are respectively reduced from 387.8 MPa and 18.6% to 348.9 MPa and 13.9%. After further peak-aging at 120 °C for 24 h, numerous G.P. II zone and η′ phase precipitate in matrix. Consequently, UTS values of the surface and interior increase to 449.5 and 421.4 MPa, while elongation values decrease to 12.5% and 8.1%, respectively.     

Effect of Mg composition on sintering behaviors and mechanical properties of Al–Cu–Mg alloy

Al–3Cu–Mg alloy was fabricated by the powder metallurgy (P/M) processes. Air-atomized powders of each alloying element were blended with various Mg contents (0.5%, 1.5%, and 2.5%, mass fraction). The compaction pressure was selected to achieve the elastic deformation, local plastic deformation, and plastic deformation of powders, respectively, and the sintering temperatures for each composition were determined, where the liquid phase sintering of Cu is dominant. The microstructural analysis of sintered materials was performed using optical microscope (OM) and scanning electron microscope (SEM) to investigate the sintering behaviors and fracture characteristics. The transverse rupture strength (TRS) of sintered materials decreased with greater Mg content (Al–3Cu–2.5Mg). However, Al–3Cu–0.5Mg alloy exhibited moderate TRS but higher specific strength than Al–3Cu without Mg addition.     

Effects of extrusion temperature on microstructure evolution and mechanical properties of heterogeneous Mg−Gd alloy laminates via accumulated extrusion bonding

The influence of extrusion temperature on microstructure and mechanical properties of heterogeneous Mg?1Gd/Mg?13Gd laminate prepared by accumulated extrusion bonding was investigated. The results reveal that the Mg?1Gd/Mg?13Gd laminate forms a significant difference in grain size between the successive layers when extruded at 330 °C, and this difference gradually disappears as the extrusion temperature increases from 380 to 430 °C. Besides, the growth rate of recrystallized grains in fine-grained layers is faster than that in coarse-grained layers. Moreover, the diffusion ability of Gd element increases with elevating extrusion temperatures, promoting the increase and coarsening of precipitates in fine-grained layers. Tensile tests indicate that the sample extruded at 380 °C has a superior combination of strength and ductility. This is mainly attributed to the synergy of the heterogeneous texture between coarse and fine-grained layers, hetero-deformation induced strengthening and hardening. The fine-grained layers facilitate the activation of prismatic 〈a〉 slips, while coarse-grained layers make it easier to active basal 〈a〉 and pyramidal 〈c+a〉 slips, especially for the sample extruded at 380 °C. The activation of pyramidal 〈c+a〉 slips contributes to coordinating further plastic deformation.     

Effect of Y on microstructure evolution and mechanical properties of Mg−4Li−3Al alloys

To obtain magnesium alloys with a low density and improved mechanical properties, Y element was added into Mg−4Li−3Al (wt.%) alloys, and the effect of Y content on microstructure evolution and mechanical properties was investigated by using optical microscopy, scanning electron microscopy and tensile tests. The results show that mechanical properties of as-cast Mg−4Li−3Al alloys with Y addition are significantly improved as a result of hot extrusion. The best comprehensive mechanical properties are obtained in hot-extruded Mg−4Li−3Al−1.5Y alloy, which possesses high ultimate tensile strength (UTS=248 MPa) and elongation (δ=27%). The improvement of mechanical properties of hot-extruded Mg−4Li−3Al−1.5Y alloy was mainly attributed to combined effects of grain refinement, solid solution strengthening and precipitation strengthening.     

Effects of extrusion and heat treatments on microstructure and mechanical properties of Mg–8Zn–1Al–0.5Cu–0.5Mn alloy

The effects of extrusion and heat treatments on the microstructure and mechanical properties of Mg–8Zn–1Al–0.5Cu– 0.5Mn magnesium alloy were investigated. Bimodal microstructure is formed in this alloy when it is extruded at 230 and 260 °C, and complete DRX occurs at the extruding temperature of 290 °C. The basal texture of as-extruded alloys is reduced gradually with increasing extrusion temperature due to the larger volume fraction of recrystallized structure at higher temperatures. For the alloy extruded at 290 °C, four different heat treatments routes were investigated. After solution + aging treatments, the grains sizes become larger. Finer and far more densely dispersed precipitates are found in the alloy with solution + double-aging treatments compared with alloy with solution + single-aging treatment. Tensile properties are enhanced remarkably by solution + double-aging treatment with the yield strength, tensile strength and elongation being 298 MPa, 348 MPa and 18%, respectively. This is attributed to the combined effects of fine dynamically recrystallized grains and the uniformly distributed finer precipitates.     

Microstructure evolution and mechanical properties of Al−3.6Cu−1Li alloy via cryorolling and aging

An Al−3.6Cu−1Li alloy was subjected to room temperature rolling and cryorolling to investigate their effects on microstructure evolution and mechanical properties. The microstructure and aging characteristics of the room temperature-rolled and the cryorolled alloys with 70% and 90% of thickness reductions were studied by microstructure analysis and mechanical tests. The samples subjected to cryorolling with 90% of thickness reduction have high strength and good toughness. This is mainly due to the inhibition of dynamic recovery and the accumulation of high-density dislocations in cryorolled samples. In addition, the artificial aging reveals that the temperature at which peak hardness is attained is inversely proportional to the deformation amount and directly proportional to the rolling temperature. Moreover, bright field images of cryorolled samples after aging indicate the existence of T1 (Al2CuLi) precipitates. This suggests that the high stored strain energy enhances the aging kinetics of the alloy, which further promotes the nucleation of T1 phases.     

Effects of cooling rate on microstructure,mechanical and corrosion properties of Mg–Zn–Ca alloy

Mg₆₉Zn₂₇Ca₄ alloys with diameters of 1.5, 2 and 3 mm were fabricated using copper mold injection casting method. Microstructural analysis reveals that the alloy with a diameter of 1.5 mm is almost completely composed of amorphous phase. However, with the cooling rate decline, a little α-Mg and MgZn dendrites can be found in the amorphous matrix. Based on the microstructural and tensile results, the ductile dendrites are conceived to be highly responsible for the enhanced compressive strain from 1.3% to 3.1% by increasing the sample diameter from 1.5 mm to 3 mm. In addition, the Mg₆₉Zn₂₇Ca₄ alloy with 1.5 mm diameter has the best corrosion properties. The current Mg-based alloys show much better corrosion resistance than the traditionally commercial wrought magnesium alloy ZK60 in simulated sea-water.     

Effect of Gd content on microstructure and dynamic mechanical properties of solution-treated Mg−xGd−3Y−0.5Zr alloy

The effect of Gd content ranging from 6.5 wt.% to 8.5 wt.% on microstructure evolution and dynamic mechanical behavior of Mg?xGd?3Y?0.5Zr alloys was investigated by optical microscopy, X-ray diffraction, scanning electron microscopy and split Hopkinson pressure bar. The microstructure of as-cast Mg?xGd?3Y?0.5Zr alloys indicates that the addition of Gd can promote grain refinement in the casting. Due to the rapid cooling rate during solidification, a large amount of non-equilibrium eutectic phase Mg₂₄(Gd,Y)₅ appears at the grain boundary of as-cast Mg?xGd?3Y?0.5Zr alloys. After solution treatment at 520 °C for 6 h, the Mg₂₄(Gd,Y)₅ phase dissolves into the matrix, and the rare earth hydrides (REH) phase appears. The stress?strain curves validate that the solution-treated Mg?xGd?3Y?0.5Zr alloys with optimal Gd contents maintain excellent dynamic properties at different strain rates. It was concluded that the variation of Gd content and the agglomeration of residual REH particles and dynamically precipitated fine particles are key factors affecting dynamic mechanical properties of Mg?xGd?3Y?0.5Zr alloys.