Improvement of elevated-temperature strength and recrystallization resistance via Mn-containing dispersoid strengthening in Al-Mg-Si 6082 alloys

Enhanced Elevated-Temperature Strength and Creep Resistance of Dispersion-Strengthened Al-Mg-Si-Mn AA6082 Alloys through Modified Processing Route

“…By contrast, homogenization at a higher temperature before extrusion negatively impacts the dispersoid size and number density [ 8 , 13 , 16 ]. For instance, although extruded at 350 °C, the dispersoids formed during high-temperature homogenization (550 °C/5 h) in 0.5Mn(HL) featured a much larger and lower after extrusion compared to the dispersoids formed during low-temperature homogenization (400 °C/5 h) in 0.5Mn(LL), as shown in Table 2 .…”

“…Apparently, the very coarse dispersoids in 0.5Mn(HL) ( Table 2 ) were incapable of retarding SRX. By contrast, both 0.5Mn(LL) and 1Mn(LL) remained resistant to SRX at 540 °C, and the microstructures under both conditions were still deformed recovery structures ( Figure 3 c,d) owing to the higher Zener pinning effect caused by the fine and densely distributed dispersoids [ 13 , 16 ]. In addition, compared with the grain structure in 0.5Mn(LH) ( Figure 2 a), the 0.5Mn(LL) after solution treatment ( Figure 3 c) still had a higher density of dislocations and LAGBs.…”

“…Furthermore, the number density (N v ) in 1Mn(LL) after solutionizing was remarkably higher than that in 0.5Mn(LL) (588 µm −3 vs. 387 µm −3 ) with a comparable size of ≈33 nm (Table 2), resulting from the higher Mn content in 1Mn(LL). By contrast, homogenization at a higher temperature before extrusion negatively impacts the dispersoid size and number density [8,13,16]. For instance, although extruded at 350 • C, the dispersoids formed during high-temperature homogenization (550 • C/5 h) in 0.5Mn(HL) featured a much larger D and lower N v after extrusion compared to the dispersoids formed during low-temperature homogenization (400 • C/5 h) in 0.5Mn(LL), as shown in Table 2.…”

“…These research efforts are generally driven by the relatively high maximum solubility of Mn in α-Al and its affordability compared to other slow-diffusing transition metals, such as Sc and Zr [ 10 ], which are used to enhance the high-temperature strength of Al alloys. The β′-MgSi precipitates formed during heating to the homogenization temperature in an Al-Mn-Mg alloy act as effective nuclei for α-Al(FeMn)Si dispersoids [ 11 , 12 ], thus substantially increasing their number density [ 13 ]. Moreover, a new low-temperature homogenization process was established to obtain a high number density of fine α-Al(FeMn)Si dispersoids while exhibiting enhanced Orowan strengthening and Zener drag effects [ 7 , 8 , 14 ].…”

“…Our recent study [ 8 ] has shown that dispersoids become very prone to coarsening during a typical extrusion process of 6082 alloy, and their average sizes almost double after extrusion compared with that after homogenization at a relatively low temperature (400 °C). Therefore, decreasing the extrusion temperature to below 400 °C in combination with low-temperature homogenization, at which both the diffusivity of Mn in Al and the coarsening of α-Al(FeMn)Si dispersoids are rather limited [ 13 , 15 ], might further retard the coarsening of dispersoids and provide a higher Orowan strengthening effect after the final processing stage.…”