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.

Hot tearing behavior of NZ30K Mg alloy under progressive solidification

Progressive solidification is usually considered an effective strategy to reduce the hot tearing susceptibility of a cast component.In this study,special constrained plate castings with progressive changes in cross-section were designed,which enabled progressive solidification.The hot tearing behavior of a newly developed NZ30 K Mg alloy(Mg-3.0 Nd-0.2 Zn-Zr,wt.%)was studied under progressive solidification using various mold temperature distributions and constraint lengths.Of these,a homogeneous mold temperature distribution is found to be the best option to avoid hot tearing,followed by a local low mold temperature distribution(with a chiller),then a gradient mold temperature distribution.Unexpectedly,compared with the homogeneous mold temperature distribution,adding a chiller does not provide any further reduction in the hot tearing susceptibility of the NZ30 K Mg alloy.A high mold temperature and a short constraint length increase the hot tearing resistance of cast Mg alloys.Progressive solidification is not a sufficient and necessary condition to avoid the formation of hot tearing.The two key factors that determine the occurrence of hot tearing under progressive solidification are the maximum cooling rate and the constraint length.Decreasing these values can reduce the incidence of hot tearing.

Development of High Strength and Toughness Non-Heated Al–Mg–Si Alloys for High-Pressure Die-Casting

Based on the 3 factors and 3 levels orthogonal experiment method,compositional effects of Mg,Si,and Ti addition on the microstructures,tensile properties,and fracture behaviors of the high-pressure die-casting Al-x Mg-y Si-z Ti alloys have been investigated.The analysis of variance shows that both Mg and Si apparently infl uence the tensile properties of the alloys,while Ti does not.The tensile mechanical properties are comprehensively infl uenced by the amount of eutectic phase(α-Al+Mg2Si),the average grain size,and the content of Mg dissolved intoα-Al matrix.The optimized alloy is Al-7.49 Mg-3.08 Si-0.01 Ti(wt%),which exhibits tensile yield strength of 219 MPa,ultimate tensile strength of 401 MPa,and elongation of 10.5%.Furthermore,contour maps,showing the relationship among compositions,microstructure characteristics,and the tensile properties are constructed,which provide guidelines for developing high strength and toughness Al–Mg–Si–Ti alloys for high-pressure die-casting.