Residual Stress Analysis of Additive Manufactured A356.2 Aluminum Alloys using X-Ray Diffraction Methods

The physical properties of metal-based structural materials, such as hardness, strength and toughness, are directly or indirectly affected by residual stress inside or on the surface of the given part. Repeated rapid heating and cooling during the additive manufacturing process causes thermal gradients and expansion and contraction in the material, which causes residual stress. Tensile residual stresses are known to exist on the surface of additive manufactured products and should be kept to a minimum as they affect the mechanical properties and lead to product deformation and product failure. Therefore, it is important to evaluate the residual stress after making the product and to control it under the desired conditions. There are limitations to using the destructive method commonly used for residual stress evaluation with additive manufacturing products, due to difficulties in repeated measurements, product size, and cost issues. Therefore, it is necessary to apply a non-destructive evaluation method and verify the validity of the method. In this study, A356.2 aluminum alloy powders were used for additive manufacturing using the powder bed fusion process, and the surface residual stress generated during the process was measured. X-ray diffraction (XRD) methods were used to observe the surface residual stress. After XRD measurement, analyses were performed using the Williamson-Hall plot, sin2ψ, and cosα methods. The residual stress measurement results of samples manufactured through the LPBF process and the characteristics and limitations of each method were discussed.