静轴肩搅拌摩擦增材制造2024铝合金的组织特征

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(FSAM)方法制备2024铝合金增材,用OM及SEM观察增材的显微组织,用XRD及TEM分析增材的第二相含量及形貌特征,结合增材的显微硬度,研究静轴肩FSAM材料的强化机理。结果表明:增材组织为再结晶的细小等轴晶,晶粒尺寸由底部向顶部逐渐减小,增材中的第二相发生重溶,含量较基材明显减少,且第二相含量由底部向顶部逐渐增多。增材的显微硬度由底部向顶部逐渐增大,最大硬度值为99HV,低于基材的,这是由于FSAM使增材中的第二相发生重溶,且第二相与基体的共格关系变化,共格应变减小,增材组织发生过时效。

The stationary shoulder friction stir additive manufacturing(FSAM)technology was used for additive manufacturing of 2024 aluminum alloy,the microstructure of the additive material(AM)was observed by OM and SEM,the content and morphological characteristics of the precipitated phase in the AM were analyzed by XRD and TEM.Combined with the microhardness of the AM,the strengthening mechanism of the stationary shoulder FSAM on 2024 aluminum alloy was studied.The results show that the microstructure of AM is a re-crystallized fine equiaxed grain,the grain size of the AM gradually decreases from the bottom to the top.The precipitated phase in the AM is re-dissolved,the content is significantly reduced relative to the base material(BM).The content of the precipitated phase gradually increases from the bottom to the top.The microhardness of the AM increases gradually from the bottom to the top,the maximum hardness is 99HV,still lower than that of the BM.This is because the precipitated phase in the AM is re-dissolved by the FSAM,and the coherent strain of the precipitated phase and the matrix gradually disappears,resulting in over-aging of the AM microstructure.