热处理前后选区激光熔化Al-Mn-Mg-Sc-Zr合金微观组织的演变

Microstructure Evolution of Al-Mn-Mg-Sc-Zr Alloy Prepared by Selective Laser Melting Before and After Heat Treatment

采用选区激光熔化(SLM)技术制备了Al-Mn-Mg-Sc-Zr合金。使用X射线衍射仪、扫描电子显微镜、能谱仪和透射电子显微镜等测试方法,表征了热处理前后Al-Mn-Mg-Sc-Zr合金微观组织的结构,并测试了合金的硬度。结果表明:沉积态合金组织主要由α-Al、Al6Mn和初生Al3Sc组成。SLM成形的合金熔池组织呈鱼鳞状,熔池内靠近熔合线附近形成了大量细小的等轴晶,平均晶粒尺寸约为0.57μm,熔池心部则由柱状晶组成,柱状晶的平均宽度约为0.48μm。棒状Al6Mn主要沿晶界分布,少量颗粒状的初生Al3Sc存在于晶粒内部,这表明初生Al3Sc可以作为异质形核质点,细化α-Al基体。热处理后,熔池内部等轴晶尺寸及柱状晶宽度均有所增大,组织中析出了大量细小弥散的二次Al3Sc颗粒。硬度测试结果表明,随着时效时间的延长,各温度条件下合金的硬度值呈先升高后降低的趋势,相比于沉积态合金的硬度,在325℃、180 min时效热处理后合金的硬度提高了30%左右,达到1813.0 MPa。

Al-Mn-Mg-Sc-Zr alloy was prepared by selective laser melting(SLM)technique.The microstructure of Al-Mn-Mg-Sc-Zr alloy before and after heat treatment was characterized by X-ray diffractometer,scanning electron microscope,energy dispersive spectrometer,and transmission electron microscope,and the hardness of the alloy was tested.Results show that the microstructure of as-deposited alloy is mainly composed ofα-Al,Al6Mn,and primary Al3Sc phases.The SLMed molten pool presents the fish-scale shape,and a large number of fine equiaxed crystals are formed near the fusion line of molten pool with average grain size of about 0.57μm.The center of the molten pool is composed of columnar crystals with average width of about 0.48μm.The rodlike Al6Mn phase is mainly distributed along the grain boundary,and a small amount of granular primary Al3Sc phase exists inside the grain,which indicates that the primary Al3Sc can be used as heterogeneous nuclear particle to refine theα-Al matrix.After heat treatment,the size of equiaxed crystals and the width of columnar crystals in the molten pool are increased,and a large number of fine and dispersed secondary Al3Sc particles are precipitated in the structure.The hardness test results show that the hardness of the alloy is increased firstly and then decreased with prolong the aging durations at different temperatures.Compared with that of the as-deposited alloy,the hardness of the alloy after peak aging(325℃/180 min)heat treatment increases by about 30%,reaching 1813.0 MPa.