Extrusion Behavior of Wrought and As-cast Al-5.5%Zn-2,5%Mg Alloy at Different Temperatures and Reductions Using Square Die Angle.

Abstract

 Laboratory scale extrusion experiments were carried out on AA7075 billets. Two groups of wrought and homogenized as-cast (Ф 25 X 60) mm cylindrical billets were used. Each billet was cut longitudinally into halves, the two mating surfaces were polished and scribing an orthogonal network of furrows (0.1 mm wide and 0.3 mm deep) onto one of the faces. The network formed was as a square grid of 1 mm spacing. The two halves were put together and partially extruded, removed from the die, separated along the same plane and the grid distortions were observed. 16 experiments were carried out on each group of wrought and as-cast billets. Each group 3 6 was extruded at four different pre-heating temperatures (350, 400, 420, and 450) ^oC. Four values (60, 70, 78, 95.6) % of percentage reduction in cross sectional area were used at each temperature. The ram speed was 4.6 mm/sec. A mixture of graphite powder and grease was 40 used as a lubricant. The usual type consisting of a single maximum in the transverse grid lines located at the extrusion axis was occurred in all the experiments of both groups. Microstructure tests were done on the other half after it has been extruded for all the billets of the two groups. Five positions were taken for the microstructure. The magnitude of the maximum load needed for the experiments was reported for both wrought and as-cast billets.