An indirect hot form and Quench (HFQ) for manufacturing components of aluminum alloy sheets and comparison with direct HFQ

The process of Hot Form and Quench of aluminum alloys, called Direct HFQ®, has been developed and applied to manufacture high-strength panel components, in which aluminum alloy sheet is heated to solution heat treatment temperature, quickly transferred to cold press dies, simultaneously formed and quenched, and subsequently artificially aged. For Direct HFQ, however, forming occurs at high temperatures, which results in high workpiece/die friction and wear, and hence high tooling and maintenance costs. In the present study, a novel Indirect HFQ for aluminum alloys has been proposed, in which alloy sheet in the O temper is formed at room temperature, then heated to solution heat treatment temperature, and quickly transferred to cold press dies for shape calibration and quenching, followed by artificial aging. In order to compare Indirect HFQ with Direct HFQ, AA6082 sheet specimens have been deformed uniaxially using the two HFQ techniques to a given strain or fracture. Mechanical properties of the deformed specimens have been measured, and differences in mechanical properties after the two HFQ processes have been quantified. Their microstructures have also been characterized to explain those differences. In addition, both HFQ techniques have been applied to form a B-pillar sectional component. It has been found that grain growth occurs in alloy deformed uniaxially to a strain higher than or equal to 10% during Indirect HFQ process, and the degree of grain growth decreases with increasing deformation. The grain growth during Indirect HFQ leads to a lower yield strength (up to ∼8%) and tensile strength (up to ∼12%) than that of the alloy processed using Direct HFQ. In addition, the alloy has a lower ductility and formability during Indirect HFQ than Direct HFQ.