Relationship between mechanical properties and age-hardening behavior around grain boundaries of Al-Mg-Si alloy

Nanoindentation tests were conducted near grain boundaries (GBs) of Al-Mg-Si alloy, and the influence of GB character on the aging precipitation behavior and the mechanical properties was confirmed. After obtaining the GB characters by electron back scattered diffraction (EBSD) analysis and nanoindentation tests were carried out on under-aged, peak-aged, and over-aged samples. And then, the indentation areas were observed by back scattered electrons imaging (BSE) in order to identify indentation positions near the GBs. In this study, for the GB character, focusing on the rotation angle, high-angle GBs (HAGB) and low-angle GBs (LAGB) were selected. In addition, coincident site lattice GBs (CSL) were selected as special GBs. In the 180 °C under-aged samples, the nano-hardness near GB is higher than that far from the GB, while 180 °C peak-aged samples, the nano-hardness is lower than that far from the GB. Then the range near the GB where the hardness increases, or decreases was larger at HAGB than at LAGB and CSL. This suggests that the GB character affects the aging precipitation behavior and the mechanical properties.