Abstract
7075 aluminum alloy (AA7075) in W temper, owning lower strength and higher elongation, demonstrates better formability at room temperature than the material in peak-aged T6 temper. In this work, post-forming artificial aging is used to restore the comprehensive mechanical properties of AA7075 in W-temper. A shortened artificial aging process with lower cost than the common peak aging process is proposed with the consideration of paint baking in automotive manufacturing. The effects of shortened artificial aging, peak aging, and paint baking on the mechanical properties of AA7075 are studied. Results show that the ultimate tensile strengths of AA7075 with peak aging (120 ℃/24 h) and shortened artificial aging (120 ℃/5 h) followed by paint baking (180 ℃/20 min) are both 540 MPa, and the fracture elongation is 15% and 16% respectively. Compared with peak aging, the overall mechanical property of AA7075 with shortened artificial aging treatment is slightly improved after paint baking, while the aging time is shortened by 79%, which greatly improves the production efficiency. A case study of W-temper forming of an anti-collision beam in vehicle side door is conducted. Cold forming experiments, post-forming heat treatments, and mechanical testing such as three-point bending and uniaxial tensile testing of sub-sized specimens are carried out. After paint baking, the tensile strength and maximum bending load of the AA7075 anti-collision door beams with peak aging and shortened artificial aging treatments are comparable, and a higher product of strength and elongation (about 7% increase) is achieved by shortened artificial aging. In addition, the related mechanism is discussed in terms of precipitation during peak aging, shortened artificial aging and paint baking.
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