Effect of Natural and Pre-aging on Artificial Aging of 6061 Al Alloy

6061 Al alloy is one of Al-Mg-Si alloys (6xxx series) used as cladding and structural material in research reactors because of its low nuclear absorption cross section for thermal neutrons. The artificial aging behavior of this alloy was investigated by varying the aging temperature from 120°C to 260°C and aging time from 0.5 to 64 h and is expressed in terms of hardness and tensile properties. Precipitation hardening manifests itself in 6061 Al alloy by peaks in hardness and strength either yield stress or ultimate tensile strength in their relationships with time and temperature and a drop in total elongation associated generally with intergranular fracture. The natural aging for 100 h followed by artificial aging resulted in higher yield and ultimate tensile strength and shifted the time to reach the peak strength to shorter time than the artificial aging only. Pre-aging at 100°C for 5 min followed by artificial aging at 160°C for 18 h (peak aged condition) resulted in higher yield stress, ultimate tensile strength and initial rate of strain hardening than artificial aging only.