Effect of Grain Boundary Characters on Precipitation Behavior and Local Deformation Behavior in Al-Mg-Si Alloy

Abstract

Nanoindentation tests were conducted near the grain boundary (GB) of the 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 to the GB. In this study, for the GB character, focusing on the rotation angle, the high-angle GB (HAGB) and the low-angle GB (LAGB) were selected. In addition, coincidence site lattice GBs (CSL) were selected as the special GB. In the 180℃ under-aged sample, the nano-hardness near GB is higher than that far from GB, while 180℃ peak-aged and 250℃ aged samples, the nano-hardness is lower than that far from GB. Then the amount of change in hardness of HAGB was larger than that of the LAGB. This suggests that the GB character affects the aging precipitation behavior and mechanical properties.

Fig. 3　Nano-hardness around grain boundaries at aging temperature of 180℃; (a) at under-aged around HAGB, (b) at peak-aged around HAGB, (c) at under-aged around LAGB, (d) at peak-aged around LAGB, (e) at under-aged around CSL3, (f) at peak-aged around CSL3, (g) at under-aged around CSL5 and (h) at peak-aged around CSL5.