Quantification of volume fraction of precipitates in an aged Al-1.0 mass %Mg2Si alloy

An Al-1.0 mass%Mg2Si alloy was aged at 473 K for 36 ks. Using the same samp le, resistivity (rho) measurements, tensile tests and TEM observations were carried out. The volume fraction (V-f rho) of precipitates was estimated f rom the decrement in resistivity due to aging. Length (lambda), diameter (d ) and number density (N-P) per uni: volume of the needle-shaped precipitate s were measured on TEM micrographs. Perhaps because of initiation of overag ing in the present aging condition, lambda and N-P showed a wide scatter an d differed significantly in two equivalent samples, independently heat trea ted and tested. However, proof stress and V-f rho in the two runs well coin cided with each other and the volume fraction estimated from TEM micrograph s (V-fTEM) matched within a factor of 2 for the two runs.