目前,关于激光粉末床熔合(LPBF)材料各向异性的产生机理尚未达成共识,大多数注意力都集中在晶体学结构上。在本文中,对硬度进行了分析和测试,缺陷分布,残余应力分布,LPBF制备的WE43镁合金的显微组织。结果表明,LPBFWE43表现出明显的各向异性-X-Z表面的硬度HV(平均129.9HV)和Y-Z表面的硬度HV(平均130.7HV)比X-Y表面的硬度高33.5%(平均97.6HV)。与X和Y方向相比,在堆叠方向Z上的可承受载荷较小。对各向异性贡献更大的因素依次列出如下。首先,X-Y投影表面的缺陷面积比其他两个表面的缺陷面积大约13.2%,因此,由于材料强度和缺陷数量之间的指数关系,该表面的机械性能大大降低。其次,对于每个层/时间的激光扫描,Z方向的残余应力积累高于X和Y方向,这可能会直接降低材料的机械性能。最后,与X-Y表面相比,X-Z和Y-Z表面上分布着更细的晶粒,这种细晶强化机制也有助于各向异性。经过T5时效热处理(250°C/16h),在<0001>方向上形成了更强的晶体学织构,随着取向密度指数从10.92增加到21.38,各向异性消失。这主要是由于<0001>方向的织构对Z方向的机械性能的增强作用抵消了X-Y表面的缺陷在Z方向上的弱化作用。
At present, no consensus has been reached on the generation mechanism of
anisotropy in materials fabricated by laser powder bed fusion (LPBF), and most attention has been focused on crystallographic texture. In this paper, an analysis and test were carried out on the hardness, defect distribution, residual stress distribution, and microstructure of WE43 magnesium alloy fabricated by LPBF. The results indicate that LPBF WE43 exhibits obvious
anisotropy-the hardness HV of X-Z surface (129.9 HV on average) and that of Y-Z surface (130.7 HV on average) are about 33.5% higher than that of X-Y surface (97.6 HV on average), and the endurable load is smaller in the stacking direction Z compared to the X and Y directions. The factors contributing more to the
anisotropy are listed as follows in sequence. Firstly, the defect area of the X-Y projection surface is about 13.2% larger than that of the other two surfaces, so this surface shows greatly reduced mechanical properties due to the exponential relationship between the material strength and the number of defects. Secondly, for laser scanning in each layer/time, the residual stress accumulation in the Z direction is higher than that in the X and Y directions, which may directly reduce the mechanical properties of the material. Finally, more fine grains are distributed in X-Z and Y-Z surfaces when comparing them with those in an X-Y surface, and this fine-grain strengthening mechanism also contributes to the
anisotropy. After T5 aging heat treatment (250 °C/16 h), a stronger crystallographic texture is formed in the <0001> direction, with the orientation density index increasing from 10.92 to 21.38, and the
anisotropy disappearing. This is mainly caused by the enhancement effect of the texture in the <0001> direction on the mechanical properties in the Z direction cancelling out the weakening effect of the defects in the X-Y surface in the Z direction.