Study Of Heat Treatment Mechanism Of Semi-Solid/Hot Extrusion Hypereutectic Al-Fe Alloys

In order to research the heat treatment strengthening mechanism of the hot extrusion forming/semi-solid forming of Al-Fe alloy, several groups of hypereutectic Al-5.5Fe base alloy were prepared with different components. The influence of alloying element, molding technology and heat treatment processes on microstructure and properties were analized by means of SEM, TEM and mechanical properties test detection. So the proper heat treatment scheme and strengthening mechanism with different kinds of forming process of Al-Fe alloy can be obtained.The results of the study exhibited that: alloying element can not only refine bulky needle Al3Fe phase of hypereutectic Al-5.5Fe base alloy effectively, but also form strengthening phase. This can improve the properties of the alloy. The as-cast tensile strength is 173.39MPa, but it will increase to 218.7MPa after the heat treatment of T6.With the heat extrusion process, the structure of hypereutectic Al-5.5 Fe base alloy can be refined, and bulky needle flake Al3Fe phase will change into tiny graininess. The properties of the alloy, especially for the plasticity, can enhance greatly. The tensile strength of Al-5.5Fe-4Cu-2Zn-0.4Mg-0.5Mn alloy with hot extrusion forming can reach to 275.31MPa, with its plasticity 8.17%. But with T6 heat treatment, the mechanical properties of the alloy didn't improve at all, but decreased to 165.65MPa with the plasticity not changed. The SEM exhibited the enrichment of Cu elements around the Al3Fe phase after T6 heat treatment. Further more, the behavior of the enrichment will be more obvious with the enhancement of solution temperature. According to the results of the study, the behavior of the enrichment of Cu around Al3Fe phase had nothing to do with the extrusion process parameters and other alloying element contents with changing the alloying element content and extrusion process parameters of Al-5.5Fe base alloy, but the Cu content in the alloy. After T1 heat treatment, the mechanical properties of the alloy got improved deeply, reaching to 346.8MPa. And there is no enrichment of Cu around Al3Fe phase in hot extrusion Al-5.5Fe base alloy.With the research of the heat treatment of semi-solid forming hypereutectic Al-5.5Fe, it can be concluded that the enforcing rule of heat treatment is identical with extrusion Al-5.5 Fe alloy. With T6 heat treatment, the mechanical properties of semi-solid forming Al-5.5Fe-4Cu-2Zn-0.4Mg-0.5Mn alloy and Al-5.5Fe-4Cu alloy both reduced greatly, and appears large amount of the Cu enrichment around Al3Fe phase. But with T1 heat treatment, the mechanical properties of alloy improved on a very large scale. Above all, in order to improve the properties of hypereutectic Al-5.5Fe base alloy, T1 heat treatment was more suitable but not T6.