HOT WORKABILITY OF AN AL-MG ALLOY AA5182 WITH 1-WT-PERCENT CU

A comparative study of the hot workability of two aluminium alloys, al loy AA5182 used for automotive applications and a variant modified wit h 1 wt% copper, has been carried out. Hot torsion tests were performed on both alloys subjected to two different heat treatments: a low temp erature preheat to 450 degrees C and a high temperature preheat at 540 degrees C. The results from the torsion experiments are interpreted i n terms of microstructural features. Both treatments produce the same strength, but the high temperature preheat leads to better ductility. This improvement is related to the homogenization of solute elements i n the matrix; and, concerning AA5182 + Cu, also to the dissolution of a non-equilibrium Al-Mg-Cu ternary eutectic present in the as-cast mic rostructure. The precipitation of (Fe, Mn)AI, precipitates in the matr ix of both alloys is induced by the high temperature heat treatment. C omparison of the results obtained by hot torsion shows that at low def ormation rates AA5182 + Cu has better ductility than the classical all oy, but its ductility is lower at strain rates above 0.6-0.8 s(-1). Th e null ductility transition temperature is Tower compared with that in the classical alloy, restricting the range of hot working temperature s. Inside this range the strength of both alloys is approximately the same, although the strain rate sensitivity coefficient is increased by copper additions. The experimental strength values follow the classic al sinus-hyperbolic constitutive equation for hot working.