Effect of extrusion press exit temperature and chromium on grain structure of EN AW 6082 alloy forgings

Abstract

Extruded bar is the typical forging stock in the manufacture of EN AW 6082 forged suspension components. The frictional heating and high strains introduced during extrusion leads to fine equiaxed surface grains that inevitably grow during forging owing to a very small initial grain size and a strain-free state. Higher extrusion temperatures as well as Cr addition have a favourable impact on the depth of the coarse grain zone in 6082 forgings. The interior fibrous grains may recrystallise to produce small equiaxed grains during forging and suffer abnormal growth during the solution heat treatment. Sections with entirely coarse grains appear to be the standard after the T6 heat treatment when the 6082 alloy is Cr-free regardless of the press exit temperature of the extrusion step in the production cycle. However, coarse grains are confined to the surface regions in forgings produced from 6082 alloy with as much as 0·13 wt-Cr regardless of the press exit temperature. High extrusion temperatures reduce the strain energy while Cr forms dispersoids that retard recrystallisation and grain growth during subsequent processing.

Enhancement of the Young’s Modulus through Infrared Heat Treatment: A Study of the Microstructure and the Mass Effect of Real Body 6082 Aluminum Forgings

“…The Al (FeMnCr) Si phases were in agreement with the SEM and EDS analysis results. The Mg 2 Si and Mg 5 Si 6 were the strengthen phases that formed during the aging process [4,17,18]. And this matches the result of hardness (Figure 4) and the tensile strength discussed in the next section.…”

“…Comparing with LAir, the SAir retention in the remaining metal flows occurred because SAir only solutionized for 1 h. Therefore, it could be inferred that with the solution treatment duration prolonged, non-equiaxed grains aligned in the remaining metal flows did not occur. Moreover, it has been reported that the occurrence of abnormal coarse grains is often due to the high temperature air furnace heat treatment [4] as well as the influence of fatigue properties [14]. In this study, although the IR heat treatment was performed at 560 • C, due to the efficiency of the high heat treatment, the heat treatment duration could be shortened, and therefore, no coarse grains developed.…”

“…The alloy forging process is conducted with an extruded bar and the use of pressure to shape it into the required form under a set temperature condition. During the forging process, the microstructure and the strength of the alloy changes, and the mechanical properties are improved [4]. Among them, the heat treatable 6082 aluminum alloy can be used with a subsequent heat treatment to achieve the desired mechanical material properties [5]; therefore, the heat treatment process is quite important in the 6082 forging process.…”