The microstructure regulation and property enhancement of directed energy deposited Al-Zn-Mg-Cu-Si-Zr alloy with various Zr contents

Al-Zn-Mg-Cu alloy is widely applied in the modern manufacturing industry on account of their excellent me-chanical properties. Nevertheless, the manufacturing of Al-Zn-Mg-Cu alloy by directed energy deposition (DED) remains challenging owing to the high crack sensitivity of it. In this paper, Si and Zr were added into the Al-Zn-Mg-Cu alloy as the reinforcement phases to avoid cracking and improve mechanical properties, and the effects of Zr content on the material were investigated. Cracks are completely removed in all specimens, indicating that Si is very effective on removing cracks. The average grain size first declines (Zr content <1.0 wt%) and then rises (Zr content >1.0 wt%) with the increase of Zr content, and it reaches minimum (13.8 mu m) at a mass fraction of 1.0 wt%. The changing trend of hardness, yield strength, tensile strength and elongation with Zr content is the same with average grain size, and they reach maximum (126 HV, 215.7 MPa, 333.5 MPa and 2.9%) when the Zr content is 1.0 wt%, which are further elevated (Hardness 156 HV, Yield strength 273.7 MPa, tensile strength 392.2 MPa and elongation 4.4%) after T6 treatment. It is thus verified that the incorporation of Si and Zr favors the manufacturing of Al-Zn-Mg-Cu series alloy with crack free microstructure and excellent mechanical properties.