Analysis of the bonding strength and microstructure of AA6082 extrusion weld seams formed during physical simulation

Abstract

The research was aimed to determine the effects of extrusion process condition on the weld seam quality of the aluminum alloy AA6082 by using a novel physical simulation method. A weld seam between two bars was formed under hydrostatic pressure in a specially designed die setup to simulate the longitudinal weld seam formation during extrusion through porthole die. With this die setup, extrusion process variables, i.e., temperature, extrusion speed and strain, could be varied so that their individual effects on weld seam quality could be discriminated. With the help of finite element (FE) simulation, the distributions of strains, strain rates and hydrostatic pressures inside the welding chamber were quantified. Tension tests were performed to evaluate the bonding strengths of solidstate welded samples. It was found that the amount of deformation imposed inside the welding chamber had a dominant effect on the bonding strength. A high deformation temperature and a high extrusion speed enhanced the bonding strength. The microstructures across the weld zone were examined by using a polarized light microscope and electron back-scatter diffraction (EBSD). The microstructure evolutions inside and around the welding zone were found to be influenced by the

Integrated physical and numerical simulations of weld seam formation during extrusion of magnesium alloy

“…Obviously, extrusion experiment is the most straightforward method, but it is practically impossible to get direct access to the welding chamber of the porthole die and thus difficult to gain a full understanding of the mechanisms of extrusion welding. Moreover, with this method, individual effects of extrusion process parameters on longitudinal weld seam quality cannot be studied separately (Bai et al, 2017). Numerical simulation, on the other hand, is a powerful tool to reveal the thermal and mechanical states of the deforming material and thus can be used to improve the understanding of metal flow inside the welding chamber.…”

“…A closed welding chamber was indeed able to create high hydrostatic pressure inside, which was needed for extrusion welding. Bai et al (2017) modified the die design and investigated the extrusion welding of the AA6082 aluminum alloy. The solid-state bonding strength and microstructure evolution of the alloy during physical simulation were analyzed.…”

“…To overcome the shortcomings of the die set-up for the physical simulation of extrusion welding in the precious research (Bai et al, 2017), in the present research, a modified die set-up was designed for the extrusion welding of two magnesium alloy rods. With this modified die set-up, magnesium alloy rods could be solid-state bonded inside an imitative welding chamber in an environment close to that in real extrusion through a porthole die.…”

“…A larger welding chamber (∅30×12 mm) was adopted in the present die design, compared to that (∅12 × 8mm) of the previous die (Bai et al, 2017). It provided larger space for metal streams from the two rods to flow radially (Fig.…”

“…The differences between the measured and simulated temperatures did not exceed 0.9%. The distribution of hydrostatic pressure inside the welding chamber was of critical importance for solid-state bonding occurring during extrusion (Bai et al, 2017). Fig.…”