Effect of Thermal Cycle and Temperature Gradient on Solidification Microstructure of Deposition Layer during 7075 Aluminum Alloy Laser Wire Additive Manufacturing

The 7075 aluminum alloy has found extensive application in the aerospace domain owing to its superior specific strength,low density, and remarkable resistance to corrosion. Laser wire additive manufacturing technology offers a promising solution to the challenges of intricate processing procedures, low material utilization rates, and imprecise surface finishes that characterize traditional preparation methods. This approach can facilitate the formation of 7075 aluminum alloy components with high accuracy and minimal defects in a shorter time and at a lower cost. This study involves the preparation of single-layer and single-layer multi-layer laser wire additive deposition layers of 7075 aluminum alloy using various process parameters. The temperature field distribution and microstructure of the deposited layer are analyzed systematically in this study using the finite element method, with a particular focus on how varying laser power levels affect them. Subsequently, the study elucidates the influence mechanism of the microstructure variation caused by heat input on the hardness of the 7075 aluminum alloy deposit. The results show that when the laser power is increased from 1 600 W to 2 200 W, the peak temperature of the molten pool increases by 12.5% and the temperature gradient decreases from 62.8 ℃/mm to 12.4 ℃/mm. Simultaneously, an increase in the high temperature zone area of the deposition structure is observed, along with a 20.85% rise in the melting width. The peak temperature increase of the single-channel multi-layer deposition layer is greater than that of the single-layer single-channel deposition layer. The grain size in the upper, middle, and lower parts of the deposition layer grows as the laser power is raised. Moreover, the second phase precipitate content at the grain boundary decreases,and the deposition layer experiences a columnar to equiaxed crystal transition from its bottom to the top. The microhardness of the deposited samples is greater than 90 HV at various positions and laser power levels.