搅拌摩擦加工速度对再生铝合金组织和性能的影响

Effects of friction stir processing speed on microstructure and properties of recycled aluminum alloy

对4. 2 mm厚Al-7. 0Si-0. 85Fe-0. 30Mg再生铝合金进行搅拌摩擦加工改性,采用金相显微镜、扫描电子显微镜、万能拉伸试验机、显微硬度仪及图形分析仪等研究了加工速度对再生铝合金组织和性能的影响。研究结果表明:搅拌摩擦加工区由细小、均匀分布的球状、粒状和短棒状第二相粒子组成的中心区,边界清晰但细化效果相对较差的前进侧热机械影响区和边界不明显但保持了铸态形貌特征的返回侧热机械影响区组成。搅拌摩擦加工后,中心区的富铁相和共晶硅平均长度较基材分别减小90%和75%,而圆整度则分别提高了7倍和1. 5倍。随着加工速度的提高,富铁相细化效果和圆整度均缓慢提高,而对共晶硅的长度细化效果不敏感,但圆整度显著降低。再生铝合金的抗拉强度和伸长率最大可提高22. 1%和720%,随着加工速度的提高,其抗拉强度、屈服强度和显微硬度均呈现先增加后降低的趋势,而伸长率则逐渐降低,最大降幅达61. 8%。

The 4.2 mm thick Al-7.0 Si-0.85 Fe-0.30 Mg recycled aluminum alloy was modified by friction stir processing,and the effects of friction stir processing speed on microstructure and properties of recycled aluminum alloy were studied by microscope,scanning electron microscope,universal tensile testing machine,micro hardness tester and graphic analyzer.The results show that the friction stir processing zone is composed of central zone full with fine and uniformly distributed particles which exhibits spherical,granular and short rod-shaped,the thermo-mechanical influence zone in advance side with clear boundary but relatively poor refinement effect,and the thermo-mechanical influence zone in return side with fuzzy boundary but maintained as-cast topography.After the friction stir processing,the average length of iron-rich phase and eutectic silicon in central region is reduced by 90%and 75%,respectively,and roundness is improved 7 times and1.5 times compared to substrate,respectively.With processing speed increases,the refinement effect and roundness of iron-rich phase gradually increase,which have no sensitive refinement effect on the length of eutectic silicon,while roundness decreases significantly.The tensile strength and elongation of recycled aluminum alloy increase by 22.1%and 720%,respectively.Furthermore,with the increase of processing speed,the tensile strength,yield strength and microhardness of recycled aluminum alloy show a tendency of increase firstly and then decrease,while elongation decreases gradually with the maximum drop degree of 61.8%.