Insight into the fracture behaviour and mechanical response of ECAP processed cast and LPBF AlSi10Mg alloy

Abstract

This paper presents a comparative analysis of the microstructure, tensile deformation and fracture mechanisms of an ECAP-processed AlSi10Mg alloy produced by two different methods: selective laser melting (SLM) and casting. The evolution of the microstructure was investigated using optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). In addition, internal structural defects were analysed using X-ray computed tomography scans (CT). To investigate the mechanical properties and crack propagation during tensile deformation, a real-time visualization through in-situ tensile CT scans, along with the loading–unloading-reloading tensile test (LUR) was employed. The results showed significant differences in the mechanical property between the two ECAP-processed samples. Specifically, the SLM sample exhibited an approximately 50 % higher tensile strength of 370 MPa and a remarkable elongation at break of 12 %. Detailed microstructural analysis showed that the additional work hardening occurred mainly in the hetero-zones, where the accumulation of geometrically necessary dislocations developed back and forward stresses, which together led to the hetero-deformation induced (HDI) stresses. Further quantification of the (HDI) stress derived from the loading–unloading-reloading tensile test (LUR) confirmed origin of the additional strain hardening in the SLM specimen. Fractographic analysis showed that the poor tensile ductility of the ECAP-processed cast specimen was primarily due to the low bonding between Al and Si particles, resulting in premature fracture. In contrast, the ECAP-processed SLM specimen fractured predominantly along the softer heat-affected zones (HAZ).