A crack-free Ti-modified Al-Cu alloy processed by in-situ alloying laser powder bed fusion: Tribological behaviors and mechanical properties

Abstract

High strength Al-Cu alloys are of great interest for processing using additive manufacturing for aerospace applications. In this study, a Ti-modified Al-Cu alloy was successfully processed by in-situ alloying laser powder bed fusion (LPBF). The relationship between the volumetric energy density (VED) and the densification of a Ti-modified and unmodified Al-Cu alloy was investigated. The results showed that a high-density, crack-free Al-Cu alloy can be achieved with the addition of Ti. Hot cracks occurred along the coarse columnar grains in the unmodified Al-Cu alloy due to the severe stress concentrations arising during the LPBF process. The elimination of hot cracks was attributed to the decrease of grain size and the change of grain morphology from columnar to equiaxed with the Ti addition. The tensile properties of the Ti-modified Al-Cu alloy were significantly improved with a yield strength of 200 MPa, an ultimate strength of 289 MPa, and an elongation to failure of 8 %. The strengthening mechanisms including grain refinement strengthening, solid solution strengthening and second phase strengthening were quantified and the fracture mechanism was discussed. The tribological results showed that a low wear rate of 3.03 × 10−4 mm3 N−1 m−1 was achieved in the alloy with Ti modification, while unmodified alloy showed a poor wear resistance. The study demonstrates a novel method to develop advanced Al-Cu alloy with high density, strength and tribological resistance by in-situ alloying LPBF.