Effect of the Type of Aging after Supersaturating on Hardness and AW-7020 Stop Structure

Aluminum alloy AW-7020 is characterized by high fatigue strength. It is used primarily in welded constructions, which should be characterized by high strength and resistance to cyclically variable operational loads. They have found wide application in light welded ship constructions, bridge-carrying elements, cranes, hoists, vehicles, roof beams in roof constructions, and security barriers. The paper attempts to determine the influence of selected types of applied heat treatment on the structure and hardness of the AW-7020 alloy used in the shipbuilding industry. Heat treatment processes have been described in the aspect of improving the mechanical and strength properties of the tested alloy and its impact on ductility. Several supersaturation and aging sequences were used in the course of the study. The results of hardness tests of aluminum alloy after its earlier supersaturation and aging (natural and artificial) have been presented. Photographs of internal structures in individual sequences were taken. The obtained hardness measurement results and analysis of structures in individual states were compared with the delivery condition. To illustrate selected heat treatment processes, transient tests were also performed to accurately verify the effect of aging after saturation on hardness and changes occurring in the material structures. The results of the material tests showed that the type of heat treatment after saturation is of significant importance for the hardness and structures of the AW-7020 alloy. As a result of the research, it was proved that the tested alloy obtained in the artificial aging process more favourable strength properties, in a shorter period, compared to the use of the natural aging process.