CALPHAD aided design of a crack-free Al-Mg-Si-Ti alloy with high strength: heterogeneous nucleation and eutectic filling during additive manufacturing

The CALPHAD (calculation of phase diagrams) method was applied to facilitate the design of a crack-free Al-Mg-Si-Ti alloy fabricated by laser-powder bed fusion (L-PBF). Calculation and alloy characterisation show that Ti addition at 0.77 wt.% can offer a synergic effect of increasing the heterogeneous nucleation rate and the growth restriction factor (Q) in the initial solidification stage. Meanwhile, the increase of Mg/Si ratio can promote the formation of Al/Mg2Si eutectics to provide excellent backfilling ability in the final solidification stage. As a result, the experimental Al-Mg-Si-Ti alloy significantly improve the crack susceptibility. Also, the Al-Mg-Si-Ti alloy with dislocation interaction of Al/Mg2Si eutectics and Al3Ti particles show an excellent ultimate tensile strength of 447.8 MPa and elongation of 9.1% under as-LPBFed condition.