Effect of cold working and annealing on mechanical properties and microstructure of hot rolled Al alloy 3104

Abstract

The effect of cold rolling and subsequent annealing on the tensile mechanical properties, grain structure, and ear formation has been determined for a 3104 Al alloy. The starting material was directionally cast, hot rolled plate (440–493° C) (840–920° F) which was not completely recrystallized. This material was heated at 14° C/hr (25° F/hr) to an annealing temperature of 332° F (630° F), then held for 2 hr. This slow heating simulated that of batch annealing of rolled coils. Material in this annealed condition was cold rolled various amounts to 96% reduction in thickness, then annealed at 149–332° C (300–630° F) for up to 32 hr.

Mechanical properties were measured at 0, 45, and 90 deg to the rolling direction, and were found to be independent of orientation. For 20, 60, and 88% cold work, the material was completely recrystallized at 332° C (630° F) within 2 hr, and within one hr at 288 (550) and 316° C (600° F) for 60 and 88% cold work. At 149 (300), 204 (400), and 246° C (475° F), the material was still in the recovery region in 32 hr for 20, 60, and 88% cold work. These mechanical property results were confirmed by the microstructural examination. At 332° C (630° F), the recrystallized grain size did not increase with annealing time (up to 8 hr), and was smaller the greater the amount of prior cold work.

At 20% cold work, the ears were 0–90 deg, but were about zero at 60%, and changed to 45 deg above this value. Upon annealing at 332° C (630° F), the ears were still 0–90 deg for 20% cold work, but increased from zero to 45 deg for 60% cold work and from 45 to 0–90 deg for 88% cold work. X-ray diffraction measurements from the surface of samples of the sheets showed that the intensity of the 100 peaks decreased considerably and the 110 intensity increased slightly, consistent with the appearance of 45 deg ears. After annealing at 332° C (630° F), the intensities of both peaks increased with increasing cold work, and were about the same.