Effects Of Mn On On Microstructures And Mechanical Properties Of6061Aluminum Alloy

As one of the most important Al-Mg-Si aluminum alloys, aluminum alloy6061is widely used in mechanical parts, structural engineering, modern architecture, transportation and other fields. Materials properties were put forward to higher requirements along with development of modern industry, but aluminum alloy6061used in industry usually contains about0.2wt%Fe, the coarsed crystalline phases formed in solidification process reduce its mechanical properties, toughness and fatigue life, limit its industrial applications. Seven alloys with0.15wt%Fe and different Mn, Cr additions were designed to study the effects of the Mn content and adding methods on the crystalline phases, the recrystallization structures, aging precipitation phases and mechanical properties.The influence of Mn on the mechanical properties from microstructures was investigated and a novel6061aluminum alloy that has higher performance was suggested. The results show that:1. The existence forms of Mn, Cr in the alloys were determined:in the solidification process, Mn/Cr would be soluted in a-Al or form the coarsed Al (FeMn) Si, Al (FeCr) Si and Al (FeMnCr) Si phase; With increase of Mn content, the needlelike β-Al9Fe2Si2phase reduces whereas the Al8Fe2Si phase increases gradually, and only a-AlFeSi exists when Mn content reaches0.35%. Meanwhile the blocky-shaped Al9(MnFe)3Si phase begins to appear and increases with Mn content increased; After homogenization, the main phase in the0Mn alloy is β-Al9Fe2Si2, and that in the alloys with more than0.1wt%Mn is granular α-Al8(FeMnCr)2Si which is beneficial to the mechanical properties. The blocky Al9(MnFe)3Si phase does not change after homogenization.2. The homogenizition for6061aluminium alloy is560℃×10h, through that the compositions are homogeneous, and the nonequilibrium eutectic structures are eliminated.the grains coarsed rapidly when a higher temperature or longer time is applied.3. TEM observation showed that the α-Al15(FeMn)3Si2and α-Al15(FeMnCr)3Si2dispersed phases increase with Mn content increased, the effect of inhibitting recrystallization is enhanced, and the alloys keep the processing feature. 4. The strength of T6temper increases to maximum and then decreases with the increase of solution temperature. The solution is535℃×75mm (water quenching). Mn, Cr additions moves up the time of the peak aging, but the peak hardness shows a trend of decrease after the first increase with increase of Mn content, and the aging treatment175℃×10h is suggested.5.The T6strength increases firstly and then drops with increase of Mn Content. Comprehensive consideration suggests that the optimal content of Mn is0.2wt%, the alloy with0.2wt%Mn has improved the mechanical properties of T6temper to σb=390MPa, σ0.2=330MPa,δ=22.2%, which is increased by90MPa,55MPa and10%respectively, compared with the mechanical property standards of AA6061aluminum alloys.