Effects of heat treatments on the microstructures and mechanical properties of Mg–3Nd–0.2Zn–0.4Zr (wt.%) alloy

Microstructure and mechanical properties of as-cast and different heat treated Mg–3Nd–0.2Zn–0.4Zr (wt.%) (NZ30K) alloys were investigated. The as-cast alloy was comprised of magnesium matrix and Mg₁₂Nd eutectic compounds. After solution treatment at 540 °C for 6 h, the eutectic compounds dissolved into the matrix and small Zr-containing particles precipitated at grain interiors. Further aging at low temperatures led to plate-shaped metastable precipitates, which strengthened the alloy. Peak-aged at 200 °C for 10–16 h, fine β″ particles with DO₁₉ structure was the dominant strengthening phase. The alloy had ultimate tensile strength (UTS) and elongation of 300–305 MPa and 11%, respectively. Aged at 250 °C for 10 h, coarse β′ particles with fcc structure was the dominant strengthening phase. The alloy showed UTS and elongation of 265 MPa and 20%, respectively. Yield strengths (YS) of these two aged conditions were in the same level, about 140 MPa. Precipitation strengthening was the largest contributor (about 60%) to the strength in these two aged conditions. The hardness of aged NZ30K alloy seemed to correspond to UTS not YS.     

Effect of initial temper on the creep behavior of a Mg–Gd–Nd–Zr alloy

The effect of initial temper on the tensile creep behavior of a cast Mg–Gd–Nd–Zr alloy has been investigated. Specimens in unaged, underaged and peak-aged conditions exhibit a sigmoidal creep stage between the primary and steady-state creep stage, while the overaged specimens have no such creep stage. Transmission electron microscope observations revealed that sigmoidal creep stage was induced by the dynamic precipitation in the microstructure, and the rapid formation of β₁-phase and β-phase plates takes responsibility for the softening of material in this stage. Comparative evaluation of creep properties of the specimens showed that alloy in overaged condition had creep resistance superior to those in other conditions. Stress and temperature dependence of the steady-state creep rate were studied over a temperature range of 250–300 °C and stress range of 50–100 MPa, and a dislocation creep mechanism was proposed for the alloy.     

Effect of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y magnesium alloy

The influence of Zr on the microstructure, mechanical properties and corrosion resistance of Mg–10Gd–3Y (wt.%) magnesium alloy was investigated. The grain size of alloys decreased with Zr content from 0% to 0.93% (wt.%). The addition of Zr greatly improved the ultimate tensile strength (UTS) and the elongation (EL), while slightly improved the tensile yield strength (TYS). The UTS and the EL of the alloy containing 0.93% Zr increased by 125.8 MPa and 6.96% compared with base alloy, respectively. The corrosion resistances were found to decrease with Zr content from 0% to 0.42% and then increase from 0.42% to 0.93%. The differences in the sizes and distributions of the Zr-rich particles have significant effects on the corrosion behaviors. The alloy with 0.42% Zr addition revealed the optimum combination of mechanical properties and corrosion resistance.     

Effect of the long periodic stacking structure and W-phase on the microstructures and mechanical properties of the Mg–8Gd–xZn–0.4Zr alloys

Microstructures and mechanical properties of the Mg–8Gd–xZn–0.4Zr (x = 0, 1 and 3 wt.%) alloys, in the as-cast condition and the as-extruded condition, have been investigated. The results show that both the 14H long periodic stacking structure and the W-phase coexist together in the cast Zn-containing alloys. The volume fraction of the W-phase increases with increasing the addition of Zn. This phase is the crack source of the fracture. The 6H long periodic stacking structure is observed in the extruded Zn-containing alloys. The Mg–8Gd–1Zn–0.4Zr alloy exhibits the highest elongation, and the value of its elongation is 130% at 300 °C due to the refined microstructure. The W-phase plays an important role in improving the mechanical properties via pinning the movement of the grains at elevated temperature.     

A study on the mechanical properties of cryorolled Al–Mg–Si alloy

The mechanical properties of a precipitation hardenable Al–Mg–Si alloy subjected to cryorolling and ageing treatments are reported in this present work. The severe strain induced during cryorolling of Al–Mg–Si alloys in the solid solutionised state produces ultrafine microstructures with improved mechanical properties such as strength and hardness. The improved strength and hardness of cryorolled alloys are due to the grain size effect and higher dislocation density. The ageing treatment of cryorolled Al–Mg–Si alloys has improved its strength and ductility significantly due to the precipitation hardening and grain coarsening mechanisms, respectively. The reduction in dimple size of cryorolled Al–Mg–Si alloy upon failure confirms the grain refinement and strain hardening mechanism operating in the severely deformed samples.     

Mechanical properties of the hot-rolled Mg–12Gd–3Y magnesium alloy

Tensile and high cycle fatigue (HCF) properties of the hot-rolled Mg–12Gd–3Y (wt.%) magnesium alloy have been investigated. The magnesium alloy exhibits a fatigue strength of about 150 MPa, which is much higher than that of the commercial Mg–8Al–Zn alloy AZ80. Aging heat-treatment (T5) improved the fatigue life of the Mg–12Gd–3Y alloy. Fatigue cracks nucleated at the intense slip bands in the as-rolled alloy. After T5 treatment, however, the fatigue crack nucleation site shifted to the phase boundaries between MgGdY particles and Mg matrix. T5 heat-treatment retarded the crack initiation and thus improved the fatigue life of the Mg–12Gd–3Y alloy.     

Microstructure, mechanical properties and aging behavior of Mg–5Li–3Al–2Zn–xAg

Mg–5Li–3Al–2Zn–xAg (x = 0, 0.1, 0.3, 0.6, 1.2) alloys were prepared by medium-frequency induction furnace under the ambient of pure argon. The effect of Ag addition on the microstructure, tensile properties, and aging behavior was investigated. Results show that the addition of Ag can restrain the decomposition from MgAlLi₂ to AlLi. With the addition of Ag, the over-aging point is retarded and the over-aging phenomenon is avoided in Mg–5Li–3Al–2Zn–1.2Ag. The solid solution of Ag in matrix phases and the restraining of the decomposition from MgAlLi₂ to AlLi are two aspects that strengthen the alloys.     

Structure and mechanical properties of extruded Mg–Gd based alloy sheet

The Mg–8Gd–2Y–1Nd–0.3Zn–0.6Zr (wt.%) alloy sheet was prepared by hot extrusion technique, and the structure and mechanical properties of the extruded alloy were investigated. The results show that the alloy in different states is mainly composed of α-Mg solid solution and secondary phases of Mg₅RE and Mg₂₄RE₅ (RE = Gd, Y and Nd). At aging temperatures from 200 °C to 300 °C the alloy exhibits obvious age-hardening response. Great improvement of mechanical properties is observed in the peak-aged state alloy (aged at 200 °C for 60 h), the ultimate tensile strength (σ_b), tensile yield strength (σ_0.2) and elongation () are 376 MPa, 270 MPa and 14.2% at room temperature (RT), and 206 MPa, 153 MPa and 25.4% at 300 °C, respectively, the alloy exhibits high thermal stability.     

Microstructure and mechanical properties of Mg–Zn–Ca alloy processed by equal channel angular pressing

An ultrafine-grained (UFG) Mg–5.12 wt.% Zn–0.32 wt.% Ca alloy with an average grain size of 0.7 μm was produced by subjecting the as-extruded alloy to equal channel angular pressing (ECAP) for 4 passes at 250 °C. The fine secondary phase restricted the dynamic recrystallized (DRXed) grain growth during the ECAP processing, resulting in a remarkable grain refinement. A new texture was formed in the ECAPed Mg alloy with the {0 0 0 2} plane inclined at an angle of 58° relative to the extrusion direction. The yield stress (YS) was decreased in the as-ECAPed alloy with finer grains, indicating that the texture softening effect was dominant over the strengthening from grain refinement. The ductility of the as-ECAPed alloy was increased to 18.2%. The grain refinement caused an obvious decrease in work hardening rate in the as-ECAPed alloy during tensile deformation at room temperature.     

Mechanical properties of a two-phase alloy Mg–8%Li–1%Al processed by equal channel angular pressing

The microstructural evolution and room temperature tensile properties of Mg–8%Li–1%Al alloy processed by equal channel angular pressing (ECAP) at 403 K were investigated. It was found that the strength could be improved pass by pass. The elongation-to-failure decreased dramatically after the first ECAP pass, but could be improved pass by pass during the subsequent ECAP procedure. The microstructure analysis gave the explanations for these phenomena.     

Grain size and texture effect on compression behavior of hot-extruded Mg–3Al–1Zn alloys at room temperature

Hot-extruded AZ31 alloy was subjected to compression at room temperature. The influence of grain size and grain orientation on the compression behavior of the specimens was examined by optical microscopy, compression test and X-ray diffraction. Abundant twins activated during compression of extruded AZ31 magnesium alloy. The hot extruded AZ31 magnesium alloys had a higher Hall–Petch slope for compression than that for tension.     

Microstructure and properties of a new super-high-strength Al–Zn–Mg–Cu alloy C912

Using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the microstructure of a new super-high-strength Al–Zn–Mg–Cu alloy (C912) has been investigated. Compared with some other high-strength aluminum alloys, the C912 alloy exhibits higher strength and good stress-corrosion resistance and its specific strength is even higher than some Al–Li alloys. Its potential for use in the Chinese AE100 airplane is discussed.     

Preliminary investigations about effects of Zr, Sc and Ce additions on as-cast microstructure and mechanical properties of Mg-3Sn-1Mn (wt.%) magnesium alloy

In this paper, the effects of Zr, Sc and Ce additions on the as-cast microstructure and mechanical properties of Mg-3Sn-1Mn (wt.%) magnesium alloy were preliminarily investigated and compared. The results indicate that adding 0.36 wt.% Sc and 0.87 wt.% Ce to the Mg-3Sn-1Mn alloy, respectively leads to the formation of the extra phases of Mg-Sn-Sc and Mg₁₂Ce while adding 0.43 wt.% Zr does not cause the formation of any new phases. At the same time, adding 0.43 wt.% Zr or 0.87 wt.% Ce can refine the grains while adding 0.36 wt.% Sc coarsens the grains. Among the Zr- and Ce-containing alloys, the grains of the latter are relatively finer than those of the former. In addition, adding 0.43 wt.% Zr, 0.36 wt.% Sc and 0.87 wt.% Ce to the Mg-3Sn-1Mn alloy can improve the tensile and/or creep properties of the alloy. However, the addition of 0.43 wt.% Zr is not beneficial to the creep properties. Among the Zr-, Sc- and Ce-containing alloys, the alloy with the addition of 0.87 wt.% Ce exhibits the optimal tensile and creep properties.     

Effect of Mn on damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloy

The effect of Mn on the damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloys has been studied. The damping vs. strain amplitude spectrum of the studied alloys could be divided into three parts. The strain amplitude weakly dependent part appears again when the microplastic strain occurs at high strain amplitude. The mechanical properties of as-cast Mg–3 wt.%Ni alloy could be improved by the addition of Mn, which is due to the refinement of α-Mg dendrites and solid solution strengthening by Mn. In addition, the corrosion resistance of the alloys could also be improved remarkably by the addition of Mn.     

A novel thermal treatment on a Mg–4.2Y–2.3Nd–0.6Zr (WE43) alloy

A double-stage thermal treatment has been adopted on a Mg–Y–Nd–Zr (WE43) alloy, following suggestions of a previous calorimetric investigation. A secondary precipitation is claimed to occur at a temperature as low as 150 °C after a preliminary precipitation at 210 °C, with the effect of enhancing the hardness increase and reducing the annealing times.     

Tensile deformation behavior and mechanical properties of a bulk cast Al_(0.9) CoFeNi_2 eutectic high-entropy alloy

In this study,a new Al0.9CoFeNi2 eutectic high entropy alloy(EHEA) was designed,and the microstructures as well as the deformation behavior were investigated.The bulk cast Al0.9CoFeNi2 EHEA exhibited an order face-centered cubic FCC(L12) and an order body-centered cubic(B2) dual-phase lamellar eutectic microstructure.The volume fractions of FCC(L12) and B2 phases are measured to be 60 % and 40 %,respectively.The combination of the soft and ductile FCC(L12) phase together with the hard B2 phase resulted in superior strength of 1005 MPa and ductility as high as 6.2 % in tension at room temperature.The Al0.9CoFeNi2 EHEA exhibited obvious three-stage work hardening characteristics and high workhardening ability.The evolving dislocation substructure s during uniaxial tensile deformation found that planar slip dominates in both FCC(L12) and B2 phases,and the FCC(L12) phase is easier to deform than the B2 phase.The post-deformation transmission electron microscopy revealed that the sub-structural evolution of the FCC(L12) phase is from planar dislocations to bending dislocations,high-density dislocations,dislocation network,and then to dislocation walls,and Taylor lattices,while the sub-structural evolution of the B2 phase is from a very small number of short dislocations to a number of planar dislocations.Moreover,obvious ductile fracture in the FCC(L12) phase and a brittle-like fracture in the B2 phase were observed on the fracture surface of the Al0.9CoFeNi2 EHEA.The re search results provide some insight into the microstructure-property relationship.     

Development of extruded Mg-6Er-3Y-1.5Zn-0.4Mn (wt.%) alloy with high strength at elevated temperature

A new Mg-6Er-3Y-1.5Zn-0.4 Mn (wt.%) alloy with high strength at high temperature was designed and extruded at 350 °C. The as-extruded alloy exhibits ultimate tensile strength of 301 MPa, yield strength (along ED) of 274 MPa and thermal conductivity of 73 W/m⋅K at 300 °C. Such outstanding high-temperature strength is mainly attributed to the formation of nano-spaced solute-segregated basal plane stacking faults (SFs) with a large aspect ratio throughout the entire Mg matrix, fine dynamically recrystallized (DRXed) grains of 1–2 μm and strongly textured un-DRXed grains with numerous sub-structures. Microstructural examination unveils that long period stacking ordered (LPSO) phases are formed in Mg matrix of the as-cast alloy when rational design of alloy composition was employed, i.e. (Er + Y): Zn = 3: 1 and Er: Y = 1: 1 (at.%). It is worth mentioning that it is the first report regarding the formation of nano-spaced basal plane SFs throughout both DRXed and un-DRXed grains in as-extruded alloy with well-designed compositions and processing parameters. The results provide new opportunities to the development of deformed Mg alloys with satisfactory mechanical performance for high-temperature services.     

Thermal stability and mechanical properties of nanostructured Ti–24Nb–4Zr–7.9Sn alloy

Thermal stability of the nanostructured grains of cold-rolled Ti–24Nb–4Zr–7.9Sn alloy and corresponding variations in mechanical properties were investigated. The activation energy for grain growth was found distinct below and above the ( + β)/β transus of 950 K, with values of 47 and 206 kJ/mol, respectively. Due to the pinning effect of the precipitates at β grain boundaries, grains sizes can be maintained at less than 100 nm during prolonged annealing at temperatures up to 773 K, and are less than 1 μm for annealing temperature up to 923 K and time up to 2 h. Annealing above the β transus resulted in coarse grains with sizes of tens of micrometers in less than 2 h. Tensile and hardness tests showed rapid strengthening with the increase of annealing time below 773 K, which was attributed to both the rapid formation of nano-sized precipitates and the slow growth rate of β grains. By adjusting the grain size of the cold-rolled material the high strength/low Young's modulus match desirable for implant applications can be improved over the hot-rolled bars with coarse grains.