Selective laser melting of 7075 aluminum alloy inoculated by Al–Ti–B: Grain refinement and superior mechanical properties

Abstract

Coarse column grain and hot cracking severely hinder the application of AA7075 aluminum alloy fabricated by selective laser melting (SLM). In this work, a novel grain refiner consisting of submicron TiH2 and amorphous B particles was developed to control such features in SLM-fabricated AA7075 alloy. Crack-free and dense (TiH2+B)/AA7075 alloy was fabricated under optimal SLM processing. Results show that the addition of TiH2 and B particles can convert coarse columnar grains into homogeneous equiaxed grains, decrease the average grain size from 29.1 μm to 2.3 μm, and consequently eliminate the hot-cracking in (TiH2+B)/AA7075 alloy. The remarkable grain refinement is mainly attributed to heterogeneous nucleation promoted by a combination of in-situ formed L12-Al3Ti and TiB2 nanoparticles. After T6 heat treatment, the (TiH2+B)/AA7075 alloy behaves superior mechanical properties(tensile strength of ∼582 MPa and ductility of ∼12.8%) to most previously reported SLM-fabricated 7075 alloys. Synergetic effects of crack elimination, grain refinement, and precipitation strengthening are responsible for the excellent mechanical properties.