Morphology And Controlling Of The Second Phase In The Wear-Resistant AlSiFe Alloy

In the thesis, the microstructual characters of Al-20Si-5Fe alloy and the influence of the solidifying conditions and alloying elements on the second phase morphology are studied systematically, which is done to change the second phase morphology by alloying and controlling the solidification conditions so as to make the second phase refined by semi-solid or solid extruding forming technology.The influences of the alloying elements of Mn, Ti, RE, alternating current field (ACF), electromagnetic stirring and reheating on the morphology of the second phase of Al-20Si-5Fe alloy are studied thoroughly. The studying results indicate that:In the Al-20Si-5Fe alloy, the primary silicon and the rich iron-phase have the very large size and the eutectic structure become long acicular structure. Adding the different amount of alloying elements Mn and Ti to the Al-20Si-5Fe alloy makes the primary silicon and the rich iron-phase refined very well. That the alloying element Mn and Ti substitutes the atom of Fe in the rich iron-phase (Al,Si,Fe) and resumes the part of the element Si in primary phase refines the second phase. At the same time, the volume percentage of second phase is increased.At the course of solidification, the alternating current field changes obviously the microstructure morphology of the Al-20Si-5Fe-X alloy and the number of particle eutectic structure is increased. Influenced by the alternating current field, except that a little of eutectic iron-phase still is the acicular structure, the most of eutectic iron-phase of the Al-20Si-5Fe-Mn alloy is refined into tiny particles which is segregated. Influenced by the alternating current field, all of the eutectic microstructure of Al-20Si-5Fe-Ti alloy changed into very small particles which is well-distributed on the base of a -Al. Electromagnetic stirring stimulates the forming of equiaxed crystal in Al-20Si-5Fe-Mn alloy. Primary iron-phase is transformed from thick needle into smooth block. Eutectic iron-phase is shortly acicular.The morphology of second phase in the alloy is not uniform if the alloy is preserved at the same temperature for the different time. The longer the time of heat preservation is, the finer the second phase is.The second phase of alloy changes very much for the reheating. All of the primary silicon and iron-phase in Al-20Si-5Fe-3Mn alloy is transformed into little well-distributed block. The primary silicon of Al-20Si-5Fe-xTi alloy is refined well and intends to ball. The iron-phase changes to short needle. The result of Al-20Si-5Fe-1.5Ti alloy is evident.After the plasticity deformation, b of AI-20Si-5Fe-3Mn and Al-20Si-5Fe-1.5Ti alloys influenced by the alternating current field is improved by 46.70% 38.01% respectively much more than the Al-20Si-5Fe alloy.