Microstructure and mechanical properties of high strength Mg−15Gd−1Zn−0.4Zr alloy additive-manufactured by selective laser melting process

In order to verify the feasibility of producing Mg−rare earth(RE)alloy by selective laser melting(SLM)process,the microstructure and mechanical properties of Mg−15Gd−1Zn−0.4Zr(wt.%)(GZ151K)alloy were investigated.The results show that fine grains(~2μm),fine secondary phases and weak texture,were observed in the as-fabricated(SLMed)GZ151K Mg alloy.At room temperature,the SLMed GZ151K alloy has a yield strength(YS)of 345 MPa,ultimate tensile strength(UTS)of 368 MPa and elongation of 3.0%.After subsequent aging(200℃,64 h,T5 treatment),the YS,UTS and elongation of the SLMed-T5 alloy are 410 MPa,428 MPa and 3.4%,respectively,which are higher than those of the conventional cast-T6 alloy,especially with the YS increased by 122 MPa.The main strengthening mechanisms of the SLMed GZ151K alloy are fine grains,fine secondary phases and residual stress,while after T5 treatment,the YS of the alloy is further enhanced by precipitates.

Effect of double aging on mechanical properties and microstructure of EV31A alloy

To improve the ductility of a commercial Mg−rare earth alloy EV31A(Mg−3Nd−1.5Gd−0.3Zn−0.5Zr),a heat treatment method called double aging is explored,and its effect on mechanical properties and microstructure of the alloy is studied.Ultimate strength and elongation of the alloy can be increased to 288 MPa and 6.6%by the optimum double aging process,compared to 273 MPa and 4.9%after single aging.Time consumption of the aging process is also significantly decreased from 16 h(single aging)to 2 h.HAADF-STEM characterization shows that the primary precipitate isβ'phase,which is similar toβ'phase in Mg−Nd binary alloy.By double aging,theβ'phase is finer and more densely distributed compared with single aging,with approximately double density and half size,which explains the improvement in strength and ductility.

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 ℃ 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 ℃. 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 ℃.

Effects of annealing on mechanical properties and degradation behavior of biodegradable JDBM magnesium alloy wires

Mg−Nd−Zn−Zr magnesium alloy(JDBM)has been studied widely as biodegradable medical material.To process high quality JDBM wires,effects of annealing on the mechanical properties and degradation behavior after drawing were studied by microscopic observations,tensile and immersion tests.The as-extruded wires with a diameter of 3 mm could be drawn up to 9 passes without annealing until 125%cumulative drawing deformation.Complete recrystallization occurred after annealing at 325℃ for 30 min,350℃ for 5 min or 450℃for 3 min,respectively.Room temperature tensile tests and simulated body fluid immersion tests showed that annealing at slightly elevated temperature for short time could obtain better properties due to the finer grain size and more dispersive distribution of precipitates.For this study,annealing at 350℃ for 5 min is the best parameters which can be utilized to further fabricate fine wires.

Microstructure evolution and mechanical properties of rheo-processed ADC12 alloy

Microstructure evolution and mechanical properties of the rheo-processed ADC12 alloy were investigated by means ofoptical microscopy, X-ray diffraction and scanning electron microscopy. Primary dendritic Al of rheo-casting (RC) andrheo-diecasting (RDC) ADC12 alloys are sheared off. The average size, as well as solid fraction of the primary Al increase withdescending pouring temperature. The mechanical properties of alloys are strengthened by rheo-processing. Ultimate tensile strengthsof RC samples increase with the decrease of the pouring temperature, and reach the maximum in the range from 580 to 600 °C. Atpouring temperature of 595 °C, the RDC sample obtains the best ultimate tensile strength and elongation. Great reductions onporosity and primary Al globularization are crucial to the mechanical properties. Relationships of the primary Al size and yield stressare depicted with Hall?Petch equation.

Cu对铸造Al-Si-Cu合金组织和力学性能的影响

通过金属型铸造制备了Al-Si-Cu合金,结合扫描电镜和能谱仪对合金的组织进行分析,对不同热处理状态下的合金进行力学性测试,研究了Cu对铸造Al-Si-Cu合金组织和力学性能的影响,并通过热分析确定了合金的最佳热处理工艺。结果表明,试验优化后的Al-Si-Cu合金铸造性能优良,热处理后其力学性能得到大幅提升。当Cu含量在0.6%-3.5%之间时,随着Cu含量的增加,合金中Al2Cu相和Q-Al5Cu2Mg8Si6相增加,合金的力学性能有明显提高,抗拉强度增幅最高达17%,而伸长率下降。