On the Si-induced microstructure evolution, solidification cracking healing and strengthening behavior of laser powder bed fusion additive manufactured Al-Cu-Mg/Si alloys

Abstract

Severe hot-cracking behavior is a crucial challenge for the further development of high-strength aluminum alloys processed by laser powder bed fusion (LPBF). In the present study, compositional modification with addition of 2.04 wt% Si to Al-Cu-Mg alloy was performed to avoid hot cracking and enhance tensile performance. The effect of Si on hot-cracking resistance, microstructure evolution, interactional behavior with Cu and Mg, and precipitation behavior was explored. The LPBF processing window of the Al-Cu-Mg alloy is enlarged after introducing 2.04 wt% Si, and the threshold laser scanning speed for hot cracking in the Si-modified Al-Cu-Mg alloy increases to 400 mm/s. The trapping behavior of Cu in α-Al matrix and segregation of Mg into interdendritic regions occur in the solidification process because of the Si-induced variation in kCuR and kMgR. The addition of Si refines the columnar grains by increasing the value of growth restriction factor (Q) and promotes the formation of Mg2Si at grain boundaries, both of which are conducive to improving the hot-cracking resistance. For the Si-modified Al-Cu-Mg alloy, a high volume fraction of S′ phase because of the accelerated precipitation kinetics and novel Q′ phase obviously enhanced the tensile performance. Moreover, the trade-off behavior of the Al-4.41Cu-2.42Mg alloy was broken once 2.04 wt% Si was added, with the yield strength (YS) and elongation (EI) increasing from 234.7 ± 9.6 MPa, and 2.6 ± 0.1% to 320.1 ± 14.3 MPa, and 4.1 ± 0.7%, respectively.