The microstructure tailoring and property improving of directed energy deposited Al-Zn-Mg-Cu alloy modified with various Si and ZrO2 contents

Al-Zn-Mg-Cu alloys are traditional lightweight materials with extraordinary mechanical properties. Nevertheless, the manufacturing of Al-Zn-Mg-Cu alloys by directed energy deposition (DED) technique is still a tough problem since these alloys are prone to hot-cracking during the rapid solidification process of DED. In this paper, the co incorporation of Si and ZrO2 into the Al-Zn-Mg-Cu alloy was adopted for alleviating solidification shrinkage and enhancing mechanical properties. After the addition of Si, cracks are completely eliminated and the microstructure is refined due to the formation of Si rich eutectic phases. The average grain size is further decreased when ZrO2 was added and the elevation of ZrO2 amount facilitates the declination. The combined effects of Si and ZrO2 induce the enhanced tensile properties (241 MPa in tensile strength, 160 MPa in yield strength and 4.1% in elongation) of the Al-Zn-Mg-Cu alloy modified with 2.9 wt% Si and 1.5 wt% ZrO2, which are further improved after T6 treatment (304 MPa in tensile strength, 225 MPa in yield strength and 4.3% in elongation). This paper indicates that the present approach can enable the manufacturing of crack free hard-to-weld Al-ZnMg-Cu alloys with ultrafine grains by DED through adding appropriate ceramic inoculants.