Study On The Microstructure And Properties Of Al-Mn Alloy

In this study,the effects of different modifiers on the primary phase of Al-2.5Mn alloy were studied and the modification mechanism was analyzed preliminarily.In addition,three kinds of new alloys were designed and tested,and got good comprehensive properties.The results show that Cr could improve significantly the size and morphology of the primary phase of Al-2.5Mn alloy.When the Cr content was 0.35%,the phases in the upper of the alloy were Al₆Mn and Al₃Mn that were very fine;when the Cr content was more than0.35%,the microstructure of alloy were coarsening.The larger massive phase at the bottom of the alloy was Al₈₅Mn₇Cr₈,but it was much finer than that without Cr.And the height of the precipitation layer contained of the massive phase precipitated at the bottom was about 5 mm.According to the analysis,the main reason was the formation of the Al₈₅Mn₇Cr₈ precipitation that Cr participated,which increased the density of the phase.Moreover,the phase would be further promoted to sink due to the size and morphology of the phase containing Cr.After testing,the conductivity of Al-2.5Mn-0.35Cr alloy in the bottom was obviously lower than that in the upper.Therefore,it was considered that the conductivity of Al₈₅Mn₇Cr₈ was poor.Moreover,the liquidus temperature of Al-2.5Mn-0.35Cr alloy reached 671.8?,which will increase the solidification range of the alloy and will future reduce the fluidity of the alloy,so that the feeding capacity of the alloy was decreased during pouring.Sr could also improve significantly the size and morphology of the primary phase of Al-2.5Mn alloy.When the content of Sr was more than 0.35%,the phases in the upper were the eutectic microstructures of Al₆Mn and Al₄Sr.However,with the increase of Sr content,the number of Al₄Sr?needle-like?in the upper of the alloy increased gradually and tended to grow.There was a large concentrated and massive phases in the bottom of the alloy that were finer than that in some alloys without Sr.Therefore,Sr could refine the massive phase.The combined modification of Sr,Cr and Al-Ti-B was good.Microstructures in the alloy containing Ti or B were not detected,and they were thought to exist in the form of nucleation core.With the increase of Al-Ti-B content,the microstructure and grain size of the alloy could be refined.The Al₄Sr phase became shorter and finer,and the Al Mn phase was broken from continuous grid-like to discontinuous.The average strength of the three alloys after adjustment was 166.7MPa,104.8MPa and110.4MPa respectively,and the elongation is 32.9%,36.1%and 34.4%respectively.All of alloys had good comprehensive properties and different advantages in production cost,heat resistance and strength.