To improve robustness of mechanical properties of semi-solid cast A356 alloy using taguchi design method

Mechanical properties of semi-solid casting are dependent on multiple processing parameters,and improper processing parameters will not only reduce mean data but also increase variations.The present study investigated the impact of parameters in slurry preparation and heat treatment on the yield strength and ductility of T6 heat-treated A356 Al-Si alloy using rapid slurry forming(RSF)semi-solid casting.The focus was primarily on the robustness of mechanical properties based on Taguchi design method.By analyzing signal-to-noise ratio and minimum value calculated from-3S,the optimum slurry preparation parameters and heat treatment parameters were determined to be no quench,enthalpy exchange material(EEM)temperature of 140℃,EEM-to-melt ratio of 6mass%,stirring time of 18 s,solution heat treated at 520℃ for 2 h,and ageing heat treated at 190℃ for 6 h.In a small batch validation,the-3S yield strength and-3S elongation reach 256.1 MPa and 5.03% respectively,showing a satisfactory robustness.The hardness and microstructure of heat-treated samples with the best and worst properties were characterized to gain insight into the underlying mechanisms affecting the mean value and variations of mechanical properties.

一种提高镁合金零部件抗火焰蔓延性的尺寸设计类判据

基于能量守恒定律提出了一种用于预测棒状镁合金样品火焰蔓延时间的判据,该判据表明火焰蔓延时间主要受合金材料和样品尺寸影响。控制体的初始温度和起燃温度以及样品的S/l_c比值(样品横截面面积/横截面周长)是火焰蔓延时间的决定性因素。火焰蔓延时间正比于ΔH(将单位质量的样品从初始温度加热到起燃温度所需的能量)和S/l_c比值,这在Mg-8.5Al-0.5Zn-0.2Mn、Mg-2.7Nd-0.4Zn-0.6Zr和Mg-4.0Y-3.3Nd-0.5Zr镁合金中得到验证。对于尺寸相同的样品,Mg-8.5Al-0.5Zn-0.2Mn合金样品有着最大的ΔH以及最长的火焰蔓延时间;对于材质、长度和横截面面积相同的样品,圆形横截面样品的S/lc比值最大,其抗火焰蔓延性能也最佳。

Atomic relaxation,stability and electronic properties of Mg2Sn(100)surfaces from ab-initio calculations

Mg2Sn(100)surfaces were investigated using ab-initio method based on density functional theory in order to explore the surface properties.It is found that both the eleven-layers for Mg-termination surfaces and the nine-layers for Sn-termination surfaces are all converged very well.The effects of relaxation mainly occurred within the three outermost atomic layers for both Mg and Sn terminations during the surface relaxation.Mg-termination surfaces are more stable than Sn-termination surfaces according to the analysis of surface energy.The density of states reveals the metallic property of both Mg-termination and Sn-termination surfaces.Covalent bonding exists in Mg2Sn(100)surfaces according to the analysis of partial density of states.

铸造Cu−La−Zn合金的强化及导热行为

开发一种适合于压铸的高导热Cu−La−Zn合金,该合金的导热系数高达200~300 W/(m·K),约为普通黄铜的两倍。分别定量研究铸态二元Cu−La(2.0%~4.5%La,质量分数)和三元Cu−2La−xZn(0~3.0%Zn,质量分数)合金中Cu6La金属间化合物和Zn固溶原子对强化和导热行为的影响。结果表明:每增加1%(质量分数)的La或Zn,合金导热系数下降约34 W/(m·K)。Cu−2La−xZn合金中α-Cu基体的晶格常数随Zn固溶原子的增加由3.6163Å增加到3.6239Å;在Zn原子的固溶强化作用下,α-Cu基体的硬度由1.495 GPa呈抛物线增加至1.597 GPa。根据基于显微组织的Maxwell−Eucken模型计算结果,确定Cu6La的导热系数约为35.37 W/(m·K);而每增加1%Zn(摩尔分数)的固溶原子,α-Cu基体的导热系数下降51.38 W/(m·K)。

Effects of Ce content on the modification of Mg_(2)Si phase in Mg-5Al-2Si alloy

The effect of Ce content(0–1.6 wt.%)on the modification of Mg_(2)Si phase in the as-cast Mg-5Al-2Si alloy was investigated.The original Chinese script type Mg_(2)Si phase was refined distinctly and transformed to dispersive block shape gradually by adding Ce element.The length of Chinese script type Mg_(2)Si phase was reduced from 110 to 50μm with increasing Ce content to 1.6 wt.%.The results calculated by Pandat software indicated that the added Ce element first combined with Si to form CeSi_(2)phase,which could serve as the heterogeneous nucleation of Mg_(2)Si phase due to the small lattice mismatch of 7.97%.The modification of Mg_(2)Si phase was mainly attributed to the facts that Ce changed the growth steps of Mg_(2)Si phase and CeSi_(2)promoted the nucleation of Mg_(2)Si phase.With increasing Ce content from 0 wt.%to 1.6 wt.%,the YS,UTS and EL at 150℃were improved from 67.7 MPa,91.2 MPa and 1.6%to 84.2 MPa,128 MPa and 7.5%,respectively.

First-principles Calculations of Strengthening Compounds in Magnesium Alloy： A General Review

First-principles computation methods play an important role in developing and designing new magnesium alloys.In this article,we present an overview of the first-principles modeling techniques used in recent years to simulate ideal models of the structure of strengthening compounds in Mg alloys.For typical Mg compounds,structural stability,mechanical properties,electronic structure and thermodynamic properties have been discussed.Specifically,the elastic anisotropies of these compounds are examined,which is highly correlated with the possibility of inducing micro-cracks.Furthermore,some heterogeneous nucleation interfaces investigated by first-principles method are reviewed.Some of the theoretical results are compared with available experimental observations.We hope to illustrate that the first-principles computation can help to accelerate the design of new Mg-based materials and the development of materials genome initiative.Remaining problems and future directions in this research field are considered.