Sedimentation Behavior Of Iron-Rich Phase And Microstructure Modulation Of Recycled AlSi10MgFe Alloys

Since the"14th Five-Year Plan",China has introduced a number of policies to encourage the development of the recycled aluminum industry,and the recycling and reclamation of aluminum scrap is an important means to save energy,protect the environment and achieve sustainable development in China.However,in the process of waste aluminum recovery and regeneration,problems such as incomplete pretreatment and contact with iron tools during smelting often occur,which leads to the content of impurity Fe in recycled aluminum melt exceeding the standard seriously.At this time,the Fe element exists in the form of needle-likeβ-Fe phase.β-Fe phase not only severely cuts the matrix,but also is very brittle and easy to becomes a source of cracks,and is also a very active substrate for pore nucleation,which will lead to a large number of pores in the solidification organization of regenerated aluminum,significantly reducing the mechanical properties of regenerated aluminum alloy and greatly limiting the application range of regenerated aluminum alloy.Therefore,it is necessary to solve the problem of excessive content of impurity Fe elements in the melt of recycled aluminum.In this paper,the recycled Al Si10Mg Fe alloy from the factory was used as the research object.The alloys with different waste ratios were melted and regenerated,and the recycled aluminum melt was treated by adding Mn iron removal agent and combined with the melt holding process,and on this basis,the melt was modified by adding Sr densifier to further improve the mechanical properties of the recycled aluminum alloy.The effects of scrap recycle ratio,melt holding temperature and Sr addition on the iron removal rate,microstructure and mechanical properties of the recycled Al Si10Mg Fe alloy were investigated by using XRD analysis,optical microscope observation,scanning electron microscope observation,composition test,hardness test and tensile property test.The results of the study showed that:With the increase of scrap recycle ratio,the contents of Si and Fe in the Al Si10Mg Fe alloy gradually increase,and the content of Mg element decreases continuously.The coarsening degree of eutectic Si and the area fraction of theβ-Fe phase increases,the tensile strength increases first and then decreases,and the elongation decreases continuously.When the scrap recycle ratio is 25%,the tensile strength reaches the highest,which is 188.07 MPa.When the scrap recycle ratio increases to 100%,the tensile strength of the alloy decreases to171.45 MPa,and the elongation decreases to 2.03%,which decreases by 7.2%and 25.6%compared with the new alloy material,respectively.The iron removal effect of the regenerated Al Si10Mg Fe alloy is excellent when the holding temperature is 620℃and 660℃.The iron removal effect is terrible at 700℃and 740℃holding temperature.The highest iron removal rate of 35.45%is achieved in the upper layer at 660℃holding temperature.A new Fe-richα-Al₁₅（Fe,Mn）₃Si₂phase is formed in the regenerated Al Si10Mg Fe alloy after the addition of Mn iron remover.The mechanism of the influence of holding temperature on iron removal rate is that when the holding temperature is lower than the precipitation temperature of primaryα-Al₁₅（Fe,Mn）₃Si₂phase,a large number of primaryα-Al₁₅（Fe,Mn）₃Si₂phase is formed,and the sedimentation effect of iron removal is good.When holding above the precipitation temperature,the primaryα-Al₁₅（Fe,Mn）₃Si₂phase could not be generated,and there is no precipitation effect during holding.After Sr modification,the morphology of eutectic Si in the regenerated Al Si10Mg Fe alloy was changed from needle-like to fibrous and granular,and the coarse star-likeα-Fe phase was also significantly refined and transformed into Chinese character shapes.When the addition of Sr is 0.08%,the tensile strength of the regenerated Al Si10Mg Fe alloy reaches 213.25MPa,and the elongation increases to 3.87%,which is 12.1%and 27.7%higher than that of unmodified regenerated Al Si10Mg Fe alloy,respectively.With the increase of Sr addition,the fracture mode changes from brittle fracture to quasi-cleavage fracture,the crack extension path is changed and more microcracks appear.