热处理对静轴肩搅拌摩擦增材制造2024铝合金组织的影响

Effect of heat-treatment on microstructure of 2024 aluminum alloy by stationary shoulder friction stir additive manufacturing

采用静轴肩搅拌摩擦增材制造方法制备了2024铝合金增材块体,对块体进行了后续热处理,用OM观察了显微组织,用XRD及TEM分析了第二相含量及形貌特征。结合显微硬度,分析了热处理对增材块体组织及性能的影响。结果表明:增材态块体组织为再结晶的细小等轴晶,沿增材厚度方向由底部向顶部晶粒尺寸逐渐减小,第二相含量逐渐增多,显微硬度逐渐增大,最大硬度值为99 HV,平均硬度值为86.5 HV。经热处理后,增材块体中重新析出大量S′相,析出过程为α(Al)→S′(Al_(2)CuMg);第二相呈棒状和椭球状,弥散分布于α(Al)基体中,新析出的S′相与基体呈共格关系;增材块体的显微硬度明显增大,且沿厚度方向分布均匀,平均硬度值达135 HV。显微硬度明显增大的原因是热处理使增材块体中析出了细小的第二相,产生了第二相强化。

The 2024 aluminum alloy additive bulk was fabricated by the stationary shoulder friction stir additive manufacturing.Heat treatment was conducted on the addictive bulk.The microstructure was observed by OM.The content and morphology of the second phase were analyzed by XRD and TEM respectively.The effect of heat treatment on microstructure and properties of the additive bulk was analyzed under the consideration of microhardness.The results show that the re-crystallized fine equiaxed grains appear in the additive bulk sample.The grain size gradually decreases from the bottom to the top.While the content of the precipitates and microhardness gradually increase from the bottom to the top.The maximum microhardness and average microhardness values are 99 HV and 86.5 HV respectively.After heart treatment,a large number of S′phases with rod and ellipsoidal shape re-precipitated,and dispersely distribute in theα(Al)matrix,the relationship between precipitates and the matrix is coherent with each other.The process precipitation of the precipitates isα(Al)→S′(Al_(2)CuMg).More homogeneous and significantly increased microhardness are acquired,the average microhardness value is 135 HV,which should be attributed to the precipitation of a fine second phase,inducing in the precipitation strengthening.