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

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 k_Cu^R and k_Mg^R. 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.