Novel Aging Warm-Forming Process of Al-Zn-Mg Aluminum Alloy Sheets and Influence of Precipitate Characteristics on Warm Formability

Concurrently improving the formability and post-formed strength of Al-Zn-Mg alloy sheets is crucial for producing high-strength parts with complex shapes. A novel process of aging warm-forming (AWF) to form solution heat-treated and water-quenched aluminum alloy sheets is proposed in this paper. The as-quenched AA 7075 sheet was first pre-aged and then formed at the desired temperature. The automotive paint-bake process was then utilized as the second aging step to achieve the target strength of the formed part. Additionally, the post-formed strength and warm formability of specimens under the AWF process conditions, as well as the warm-forming of various heat-treated Al-Zn-Mg alloy sheets proposed in previous studies, were compared through tensile and limit dome height tests. Precipitate characteristics of specimens subjected to different warm-forming process conditions were examined to understand their impact on warm formability. The warm formability of Al-Zn-Mg alloy sheets was significantly enhanced, and the post-formed strength achieved was more than 90% of the strength of as-received AA 7075-T6 sheets under the AWF process condition. The results demonstrated the feasibility of this novel AWF process to manufacture Al-Zn-Mg alloy stamped parts for improved spring-back, formability, and good overall post-formed strength. The results also indicate that microstructural characteristics in Al-Zn-Mg alloy sheets under different warm-forming process conditions have a noticeable influence on warm formability and final mechanical properties.