Microstructure and corrosion behavior of as-homogenized and as-extruded Mg-xLi-3Al-2Zn-0.5Y alloys(x=4,8,12)

The microstructure and corrosion behavior of the as-homogenized and as-extruded Mg-xLi-3Al-2Zn-0.5Y alloys(x=4,8,12,wt.%)were studied.The results show that as the Li content increases from 4%to 12%,the matrix transfers from singleα-Mg phase,(α-Mg+β-Li)dual phase to singleβ-Li phase.A mixed corrosion feature of intergranular corrosion and pitting corrosion occurs in the Mg-4Li-3Al-2Zn-0.5Y and Mg-12Li-3Al-2Zn-0.5Y alloys.The former is related to the precipitated AlLi phase along the grain boundaries,and the latter is related to the high potential difference between the second phase and the matrix.The corrosion resistance of the as-extruded alloys is better than that of the as-homogenized alloys.The superior corrosion resistance of the as-extruded Mg-8Li-3Al-2Zn-0.5Y alloy with the lowest corrosion rate(P_(W)=(0.63±0.26)mm/a)is attributed to the more uniform distribution of second phases,the protectiveα-Mg phase via sacrificing theβ-Li phase and the relatively integrated oxide film.

Microstructure and mechanical properties of as-cast Mg-8Li-xZn-yGd(x=1,2,3,4;y=1,2) alloys

The as-cast Mg-8 Li-xZn-yGd(x=1 2, 3,4;y=1,2;wt.%)alloys were prepared in a vacuum induction furnace and their microstructure and mechanical properties were investigated. The results show that the increase of Zn content results in the volume fraction of W-phase(Mg3 Zn3 Gd2) increasing while that of Mg3 Gd phase decreasing. The strength of Mg-8 Li-xZn-1 Gd alloys is improved with the increase of Zn content,which is ascribed to the second phase strengthening of fine strip-like W-phase and the solid solution strengthening of Zn element.For Mg-8 Li-4 Zn-yGd alloys,the increase of Gd content leads to the appearance of coarse and discontinuous net-like W-phase, which decreases the strength. The Mg-8 Li-4 Zn-1 Gd alloy exhibits an optimum comprehensive performance with the yield strength, ultimate tensile strength and elongation of 154.7 MPa, 197.0 MPa and 12.4%, respectively. In addition,the aging behavior of the typical alloys was also investigated.

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 fromα-Mg toα-Mg+β-Li and then toβ-Li when the Li content increases from 4%to 14%(mass fraction).All LAZx32-0.5Y alloys contain AlLi and Al_(2)Y,while MgLi_(2)Al appears only in the alloy containing theβ-Li matrix.As the Li content increases,the content of AlLi and MgLi_(2)Al gradually increases,while the content of Al_(2)Y 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 ofα-Mg and the increase ofβ-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 MgLi_(2)Al uniformly distributed in theβ-Li matrix.

Effects of Sr addition on microstructure, mechanical properties and in vitro degradation behavior of as-extruded Zn-Sr binary alloys

The microstructures,mechanical properties and in vitro degradation behavior of as-extruded pure Zn and Zn-x Sr(x=0.1,0.4,0.8 wt.%)alloys were investigated systematically.For the microstructure and mechanical properties,Sr Zn13 phase was newly formed due to the addition of 0.1 wt.%Sr,improving the yield strength,ultimate tensile strength and elongation from(85.33±2.86)MPa,(106.00±1.41)MPa and(15.37±0.57)%for pure Zn to(107.67±2.05)MPa,(115.67±2.52)MPa and(20.80±2.19)%for Zn-0.1Sr,respectively.However,further increase of Sr content led to the deterioration of the mechanical properties due to the stress concentration and cracks initiation caused by the coarsening Sr Zn13 particles during tensile tests.For in vitro degradation,since micro galvanic corrosion was enhanced owing to the formation of the inhomogeneously distributed Sr Zn13 phase,the corrosion mode became non-uniform.Corrosion rate is gradually increased with the addition of Sr,which is increased from(11.45±2.02)μm/a(a=year)for pure Zn to(32.59±3.40)μm/a for Zn-0.8Sr.To sum up,the as-extruded Zn-0.1Sr alloy exhibited the best combination of mechanical properties and degradation behavior.

Effect of Ca content and rheo-squeeze casting parameters on microstructure and mechanical properties of AZ91−1Ce−xCa alloys

The microstructure,mechanical properties and flame resistance behavior of the AZ91−1Ce alloys with different Ca additions were firstly investigated.Then,the effect of processing parameters,including applied pressures and rotation speeds,on the microstructure and mechanical properties of the rheo-squeeze casting AZ91−1Ce−2Ca alloy was studied.The results indicate that with the increase of Ca content,the microstructure is refined and the flame resistance of the AZ91−1Ce−xCa alloys increases.But when the Ca content exceeds 1 wt.%,with the Ca content increasing,the mechanical properties of the AZ91−1Ce−xCa alloys reduce rapidly.For rheo-squeeze casting process,the increase of applied pressure and rotation speed can both bring about significant refinement in the microstructure of the AZ91−1Ce−2Ca alloy and reduction of the porosity,so the mechanical properties increase.Compared to conventional casting,the AZ91−1Ce alloy with the addition of 2 wt.%Ca by rheo-squeeze casting not only guarantees the oxidation resistance(801℃),but also improves mechanical properties.