激光选区熔化Al-Mg-Sc-Zr合金各向组织与损伤容限性能

Microstructure and damage tolerance properties in different directions of selective laser melted Al-Mg-Sc-Zr alloy

研究激光选区熔化(selective laser melting,SLM)技术成形Al-Mg-Sc-Zr合金材料不同取向的显微组织特征、拉伸和损伤容限性能。结果表明:YZ截面为细小的等轴晶和粗大的柱状晶组成的双峰组织,XY截面由细小的等轴晶组成;0°和90°方向屈服强度、抗拉强度均超过500 MPa,各向异性较小,但堆积层间存在的未熔合缺陷使得90°方向断裂伸长率明显低于0°方向;0°和90°CT试样K_(IC)分别为21.41 MPa·m^(1/2)和20.89 MPa·m^(1/2),在柱状晶区域裂纹扩展阻抗低,导致90°CT试样K_(IC)稍小;显微组织和缺陷是影响裂纹扩展性能各向异性的主要因素,在近门槛区未熔合缺陷起主导作用,当裂纹面平行于水平方向时裂纹扩展速率更快;在稳态扩展区显微组织的影响起主导作用,当裂纹面平行于水平方向时为穿晶断裂,裂纹扩展阻抗较高,裂纹扩展速率较低。

The microstructure,tensile and damage tolerance properties in different directions of Al-Mg-Sc-Zr alloy fabricated through selective laser melting(SLM)have been investigated.The results show that the YZ plane is a bimodal grain morphology composed of fine equiaxed grains and coarse columnar grains,while the XY plane is composed of fine equiaxed grains.The yield strength and tensile strength in both 0°and 90°directions are over 500 MPa,and the anisotropy is small,while the elongation in 90°direction is significantly lower than the 0°direction due to the lack of fusion(LOF)defects between the deposited layers.The K_(IC) of the 0°and 90°CT samples are respectively 21.41 MPa·m^(1/2) and 20.89 MPa·m^(1/2).The resistance to crack propagation in columnar grains region is lower and leading to a smaller K_(IC) for 90°CT samples.The microstructure and defects are the two main factors that affect the anisotropy of crack propagation performance.The LOF defects play a leading role in the near-threshold regime,and the crack propagation rate is faster when the crack propagation plane is parallel to transverse direction.On the other hand,the microstructure plays a leading role in the steady-state propagation regime.The fracture surface exhibits transgranular fracture when the crack propagation plane is parallel to transverse direction,which provides higher crack propagation resistance and result in lower crack propagation rate.