Improvement of Mechanical Properties of 3004 Aluminum Alloy by Heavy Working at Cryogenic Temperature

To improve the mechanical properties of Al alloys, grain refinement is one of the useful methods. In this study, grain refinement of 3004Al alloy was carried out by heavy plastic working i.e. warm or cryogenic forging, which induced high stored strain energy. It was possible to be rolled up to 98% reduction ratio by using cryogenic rolling with forging as prework process. Annealing was finally performed for rapid recrystallization in a salt bath at recrystallization temperature. As the result, Vickers hardness, tensile strength and yield stress of specimens worked up to 98% were HV160, 450 and 390 MPa, respectively. The specimens having annealing treatment at 583 K, 300 s produced fine grain structures with about 5 mm in grain size. It was found that the yield stress and tensile strength were 1.6 and 1.2 times compared with that of initial material regardless of forging condition. In the case of shorter annealing time, i.e. 30 s, the grain size was 3∼4 μm and yield stress increment of 2.5 times was obtained. This working process is more practical and easy to enhance its mechanical properties.