Experimental Investigation Of Primary Phase Region And Equilibrium Phase Construction At 400℃ On The 80 At.% Al Section Of Al-Mn-Mg-Zn Quaternary System

The main purpose of this work is to study the equilibrium phase relationship at 400°C and primary phase region on the 80 at.%Al section of the Al-Mn-Mg-Zn quaternary system and the liquidus projection on Al-rich part of the Al-Mn-Mg ternary system.First,we selected the alloy composition points using extrapolation calculating phase diagram from the Al-based thermodynamic database of the Thermo-Cal company.Then,we prepared Al-Mn binary master alloys in the vacuum arc furnace and sealed them with Mg and Zn elements in a vacuum tantalum tube to prepare as-cast alloys or equilibrium samples of Al-Mn-Mg ternary system and Al-Mn-Mg-Zn quaternary system through liquid-solid diffusion.After that,all samples were detected by X-ray powder diffraction（XRD）,scanning electron microscope/energy spectroscopy（SEM-EDS）,and differential scanning calorimeter（DSC）.Finally,all experimental results were analyzed comprehensively to yield following experimental conclusions:i)We deduced the liquidus projection of Al-rich part of Al-Mn-Mg ternary system,which contains Al₈Mn₅,Al₁₁Mn₄,Al₄Mn,τ₂(Al₁₈Mg₃Mn₂),Al₆Mn and Al primary phase regions.We also deduced the invaraiant reaction scheme on Al-rich part on the basis of the primary region,and the reaction temperature of invaraiant reaction L+（Al）→Al₃Mg₂+τ₂was determined to be 445℃.ii)We proposed the isothermal section at 400℃on 80 at.%Al of Al-Mn-Mg-Zn quaternary system.It has four three-phase regions:Al₄Mn+（Al）+Mg Zn₂,Al₆Mn+τ₁+Al,Al+τ₂+τ₁andτ₂+（Al）+Al₃Mg₂and two four-phase regions:Al₆Mn+Al₄Mn+τ₁+（Al）and Al₄Mn+（Al）+Mg Zn₂+Al₆Mn.None of new quaternary compound was found in the section.iii)We detected three primary phase regions:Al₁₁Mn₄,Al₄Mn andτ₂(Al₁₈Mg₃Mn₂)on the 80 at.%Al section of Al-Mn-Mg-Zn quaternary.We could not deduce any invariant reaction in the quaternary system on the basis of present experimental data.iv)According to the experimental datas,the Al-Mn-Mg-Zn quaternion Al-rich system may exit three phase reations,it is include two ternal-containing eutectic reaction:L+τ₁→（Al）+Mg Zn₂,L+（Al）→Al₃Mg₂+Al₁₈Mg₃Mn₂;One eutectic reaction:L→（Al）+τ₁（480℃）.