Synergistic Effect of Misch Metal and Al-Ti-B on the Microstructure and Mechanical Properties of 6061 Aluminum Alloy

Author of the article:CHEN Zhiqiang1,2, HU Wenxin1,2, SHI Lei2 , WANG Wei2

Author's Workplace：1. State Key Laboratory of Baiyunobo Rare Earth Resource Research and Comprehensive Utilization, Baotou 014030, China; 2. Baotou Research Institute of Rare Earths, Baotou 014030, China

Key Words：6061 aluminum alloy; rare earth; Al-Ti-B master alloy; refining effect; mechanical properties; mechanism of action

Abstract：The morphology, size and distribution of the grain and the second phase of 6061 aluminum alloy have significant effects on the comprehensive mechanical properties of the alloy. In this paper, rare earth and Al-Ti-B master alloys were added to 6061 aluminum alloy, which was used to compare grain-refining effects, investigate the manner of existence of rare earth, determine the influence and mechanism on the second phase, and analyze the influence of rare earth on the tensile properties, fracture morphology and thermal conductivity of the alloy. The results show that adding the rare earth combined with the Al-Ti-B master alloy lowers the grain size of the 6061 alloy. Rare earth elements are mainly distributed at grain boundaries in the form of the AlFeSiREMg phase and AlSiTiMgRE phase. In addition, the addition of rare earth promotes the transformation of the β-AlFeSi phase into the α-AlFeSi phase, decreases the size of Mg2Si, forms various complex compounds (e.g., AlFeSi, AlFeSiREMg and other complex compounds), and reduces the impurity of the Fe-rich phase at the grain boundary. Compared with 6061 alloy without rare earth elements, the tensile strength, elongation and thermal conductivity of 6061 alloy with 0.05% LaCe combined with 0.2% Al-Ti-B (mass fraction) master alloy are enhanced by 15.3% , 80% and 9% , respectively. Meanwhile, the rough and irregular dimples formed in the fracture morphology change into small dimples, and the form of fracture is ductile fracture.