The effects of dendritic arm spacing (as-cast) and aging time (solution heat-treated) of Al–Cu alloy on hardness

The influences of dendritic arm spacing (as-cast condition) and aging times (solution treated condition) of a hypoeutectic Al–Cu alloy on hardness are analyzed in the present study. The solidification experiments were carried out at different conditions with respect to the cooling rate during solidification: cooled molds, and uncooled chill and sand molds. In any case, mold and metal were instrumented by thermocouples. Samples were extracted from all the castings and analyzed by optical microscopy in order to have the secondary dendrite arm spacing measured. These results were correlated with the solidification cooling rate and hardness. The samples were further subjected to solution heat treatment at a temperature of 540 °C for different solution times (8, 12, 16 and 28 h), followed by quenching in water at 25 °C. A solution time of about 12 h was shown to be the best condition for the solution heat treatment. After the solution heat treatment and during natural aging, the samples were analyzed by metallography and had their hardnesses measured. Experimental laws are proposed relating the resulting hardness to the aging time.

► The influence of the as-cast structure on the solutioning of Al–Cu alloy is proposed.
► The experiments were performed utilizing chill (cooled and uncooled) and sand molds.
► Experimental laws correlating λ2 with the solidification cooling rate are proposed.
► Experimental equations are proposed relating the aging time with the hardness.