The relationship between cast structure and solution treatment of Al-Mg alloys

Abstract

The change of nonequilibrium second phase by solution treatment was obserbed particularly concerning with dendrite arm spacing. The effect of solution treatment time on the brittleness of the solution treated Al-8%Mg alloy by aging was studied. If the volume fractions of nonequilibrium second phase at times 0 and t are g₀ and g respectively, g/g₀ is expressed as:
g/g₀ = exp (kt/l₀²)
where l₀ is one-half of secondary arm spacing, and k is a constant concerning with a diffusion constant of second phase. As g₀ and l₀ are functions of cooling rate, depletion time of nonequilibrium second phase is graphically shown as a function of cooling rate. The proof stress slightly decreases, but elongation and absorbed energy greatly increase with solution treatment. The changes in elongation and absorbed energy correspond to the change of volume fraction of second phase. The longer the solution treatment time is taken, the later the time in which frac tures change from ductile to brittle becomes.