Coupling effects of SiC and TiB2 particles on crack inhibition in Al-Zn-Mg-Cu alloy produced by laser powder bed fusion

Abstract

A novel Al-Zn-Mg-Cu alloy free of cracks was produced utilizing laser powder bed fusion (LPBF) and modified with SiC and TiB2 particles. The interdependent effects of SiC and TiB2 particles on morphology, microstructure, and crystallographic texture were examined. The mechanisms behind phase evolution and crack inhibition were elucidated. The results show that a nearly dense Al-Zn-Mg-Cu alloy could be obtained when the mass fraction of SiC and TiB2 particles was 4%. TiB2 particles remained stable and acted as nucleation agents in the molten pool. Partial SiC particles reacted with the Al matrix to form rod-like Al4C3, lamellate Al4SiC4, and flocculent Si phases, which provided nucleation agents and liquid replenishment for matrix grains. The columnar grains of the matrix were refined into equiaxed grains, and the average size decreased from 37.15 μm to 7.54 μm. The preferential growth of grains along the (001) 〈001〉 direction was suppressed and transformed into a disordered random growth. The innovative Al-Zn-Mg-Cu alloy demonstrated an ultimate tensile strength of 492±12 MPa and an elongation of 7.2%±0.7%. The microhardness was enhanced, and the microhardness heterogeneity was reduced. The solidification properties were regulated, the temperature interval between solidus and liquidus was narrowed, and the liquidity of the molten pool was improved. The hot cracking of Al-Zn-Mg-Cu alloy was inhibited due to the interdependent effects of grain refinement by TiB2 particles and sufficient liquid metal replenishment by SiC particles.