Abstract
Extrusion experiments and 3D numerical modeling were conducted to investigate the dynamic recrystallization and welding quality of a 6063 aluminum alloy hollow square tube extruded by a porthole die at the ram speeds of 3 mm/s, 7 mm/s, 9 mm/s and 11 mm/s. The results showed that average grain size of hollow square tube extruded at the ram speed of 7 mm/s was the smallest. The profile extruded at the ram speed of 3 mm/s exhibited the highest expansion ratio. Dynamic recrystallization (DRX) fractions were highly variable at different ram speeds. DRX fractions in the matrix zones were higher than those in the welding zones, resulting in smaller grain sizes in the matrix zones. Mechanical properties in the welding zones and matrix zones was different. A local strain concentration would occurred during expansion, which would affect the welding quality. Finally, it was found that the uniform microstructure near the welding line would also affect the welding quality.
Highlights
The usage of lightweight and high strength materials, such as Al alloy hollow profiles, was growing
The welding quality of 6063 aluminum square tubes was studied based on the K criterion, which is in accordance with the integral in the welding path of the ratio of welding pressure to the effective stress of the billet, and can be expressed as [5]: K=
While the ram speed increased to 11 mm/s, the welding pressure slightly decreased. This was due to a higher temperature rise at a higher ram speed
Summary
The usage of lightweight and high strength materials, such as Al alloy hollow profiles, was growing. Depending on a large number of experiments and research, Donati and Tomesani [5] put forward the K criterion and found that a threshold value must be reached to obtain good welding quality These criteria have been effectively applied to evaluate welding quality, the welding process is complex during porthole die extrusion. Occurrence of DRX would influence the microstructures and mechanical properties of welding seam. The inhomogeneous DRX behavior led Materials 2021, 14, 6584 different zones during porthole die extrusion. Fan et al [8] studied the development of grains and matrix zone due to a higher DRX degree. The mechanical properties of the 6063 aluminum numporthole alloy porthole die extrusions wereBased tested.
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