Comparison of residual stresses obtained by the crack compliance method for parts produced by different metal additive manufacturing techniques and after friction stir processing

Abstract

Metal additive manufacturing (AM) techniques are promising to build complex components in automotive, aerospace and biomedical industries. However, as built AM parts generally present residual stresses which may degrade the fatigue resistance of the material. Although the AM techniques have been substantially studied, few data about the residual stress level and distribution are available in literature. This paper presents residual stress measurements and analysis on the metal powder bed AM parts using the crack compliance method. Both electron beam melting (EBM) and selective laser melting (SLM) processes are investigated for two manufactured alloys, i.e., Ti6Al4V and AlSi10Mg. It is found that: (i) the EBM process results in negligible residual stresses; (ii) the SLM leads to compressive stresses in the middle, accompanied by tensile stresses at the bottom and the top of the built part; (iii) preheating the build platform in the SLM process significantly reduces the residual stresses and effectively mitigates the porosity. Moreover, we show that post-treatment by friction stir processing inverts the residual stress distribution compared to the SLM process while significantly reducing the porosity.