Effect of rare earth Y and Al–Ti–B master alloy on the microstructure and mechanical properties of 6063 aluminum alloy

The morphology, size, and distribution of grains and secondary phases in 6063 aluminum alloy significantly influence the comprehensive mechanical properties of alloys. In this study, the rare-earth Y and Al–Ti–B master alloys were added to 6063 aluminum alloy, which is used to compare grain-refining effects, investigate the manner of existence of rare-earth Y, determine the influence and mechanism on the secondary phase, and analyze the influence of rare-earth Y on hardness, tensile property, and fracture morphology. Results revealed that adding the rare-earth Y combined with Al–Ti–B master alloy decreased the grain sizes of 6063 aluminum alloy. Rare earth Y is mainly distributed around TiB2 particles in the form of AlTiY particles, and part of it exists in α-Al grains in the form of Al3Y. Moreover, adding rare-earth Y decreased the Mg2Si size, contributed to turn β-AlFeSi phase into α-AlFeSi phase, formed various complex compounds (e.g., AlSiY, AlFeSi, and AlFeSiYMg), and reduced the impurity of Fe-rich phase at the grain boundary. Furthermore, the rare-earth Y combined with Al–Ti–B master alloy added to 6063 aluminum alloy can improve the tensile strength and elongation by 5% and 75% respectively. However, the value of hardness did not significantly change. Meanwhile, the rough and irregular dimples that formed in the fracture morphology became small dimples, and the form of fracture was ductile regardless of rare-earth Y or rare-earth Y combined with Al–Ti–B master alloy added to 6063 aluminum alloy.