Yasuhiro Aruga, Koichi Makii and Seiji Nishi
Materials Research Laboratory, Technical Development Group, Kobe Steel, Ltd., Kobe 651-2271
Al-Zn-Mg foams manufactured by a batch casting process were subjected to aging treatments with and without solution treatment. The effect of the heat treatments on matrix strength (micro-hardness) and precipitation behavior in the foams was investigated by means of transmission electron microscopy (TEM) and X-ray absorption fine structure (XAFS) analysis at a synchrotron radiation facility.
Foam aged at 398 K for 8 h after the solution treatment showed the greatest increase in strength. Fine precipitates were dispersed homogeneously and densely, which were speculated to be metastable η ' and equilibrium η phases transformed from GP zones. It is estimated that the GP zones were formed during water-quenching after the solution treatment. Overaging treatment at 423 K for 48 h after solution treatment softened the foam past its peak strength by approximately 10 in Vickers hardness. During this treatment, η ' and η phases coarsened significantly and the number density of these precipitates decreased. It is concluded that a significant drop in the strength was suppressed during overaging by the presence of a high density of the GP zones, defined as Zn-Mg ordered phases by the XAFS analysis.
aluminum foam, heat treatment, precipitation, Guinier-Preston zone (GP zone), transmission electron microscopy (TEM), X-ray absorption fine structure (XAFS)
Please do not copy without permission.