"In-situ Alloying During Laser Additive Manufacturing of AA6061 Aluminum Alloys" 

Aleena Masaeng, MSE PhD Candidate 

Advisor: Professor Xiaoyuan Lou

Zoom Link

ABSTRACT

AA6061 (Al-Mg-Si) alloys are widely used in automotive vehicle parts and structural industries due to their high strength, corrosion resistance, and weldability. However, their application in laser-based additive manufacturing is limited by a high thermal cracking susceptibility and intermetallic segregation at grain boundaries during rapid solidification. This study explores the manufacturability benefits of in-situ alloying for achieving crack-free AA6061 using laser directed energy deposition (L-DED) additive manufacturing (AM) and develops small-scale tensile test to characterize AM Al alloy samples. Given the heat-treatable nature of the alloy, the microstructural constituents are sensitive to thermal history. By using an in-situ alloying approach and preheating the substrate, crack-free AA6061 samples were successfully fabricated through the integration of optimized laser parameters. In-situ alloying improved phase uniformity, while thermal control promoted stable diffusion-driven phase transformation. The comparison between in-situ alloying and using pre-alloyed powder was discussed. Small-scale tensile tests were conducted across varied sub-size geometries. Mechanical properties were compared with literature and ASTM-E8 standards to identify geometries with comparable deformation behavior for future testing. Grain size, precipitation behavior, and mechanical properties were analyzed using different processing strategies, including in-situ alloying, heated substrate, and their combination. As-built samples were further evaluated across various post-processing conditions, such as annealed (O) and heat-treated (T6), and compared to wrought counterparts. The results show that thermal control and in-situ alloying improve the manufacturability of AA6061 via L-DED by tailoring microstructure through optimized processing. This study offers a pathway toward crack-free additive production of heat-treatable aluminum alloys.