Preparation Of Al-20Si Functionally Graded Materials Under Pulsed Magnetic Field

Functionally graded materials can overcome the problem of mismatched properties of the composite parts of the material,so that the content of components and the structure of the materials change regularly.The preparation of functionally graded materials is an important step in the study of FGM.The commonly used methods include powder metallurgy,self propagating high temperature combustion synthesis and electromagnetic phase separation.Pulsed electromagnetic field,as an electromagnetic field,has been widely used in alloy grain refinement because of its high output peak and small equipment load.This paper studies the P,Sr and RE alloying and pulse effects of magnetic treatment on the microstructure and mechanical properties of Al-20 Si alloy and on the basis of the research on the effects of pulse magnetic field and P composite effect on the distribution and morphology of primary silicon of Al-20 Si alloy.The conclusions are as follows:1)P,Sr and RE can improve the solidification structure and improve the mechanical properties of Al-20 Si alloy,among which P has the best effect on the refinement of primary silicon,and Sr has the best effect on the refinement of eutectic silicon,RE can refine primary silicon and eutectic silicon.In the range of0.0175~0.0875%,the average size of primary silicon decreases gradually with the addition of P;A new phase appeared in the alloy after adding P to AlP.In the range of0.03~0.09%,with the increasing amount of Sr eutectic silicon in Al-20 Si alloy by the long needle gradually become granular,so it has been significantly refined,and the primary silicon strip by cracking the original into petal like,which has also been refined.In the range of 0.3~0.9%,the size of primary silicon and eutectic silicon in Al-20 Si alloy decreases first and then increases with the addition of RE;When the amount of RE is 0.3%,the size of primary silicon and eutectic silicon are the most small.After adding RE element,a new phase Al3 La appears in the alloy.P and Sr,P and RE,P,Sr and RE composite can lead to the refinement of primary silicon and eutectic silicon,compound addition on primary silicon refinement effect and the addition of P alone had no significant difference,but the composite addition on eutectic silicon refining effect are better than RE or Sr alone;P,Sr and RE added alone or together added can improve the compressive strength of Al-20 Si alloy,three composite simultaneous additions lead to the highest compressive strength is 795 mpa,compared with the untreated sample,increased by 16%.2)By controlling the pulse voltage,pulse frequency,pouring temperature and preheating temperature of the pulse magnetic field,can be significantly changed the solidification structure of Al-20 Si alloy.When the pulse voltage is 80 V,the primary silicon is coarse and partial,which is concentrated at the edge of the specimen,and contains hardly primary silicon at the heart;When the pulse voltage is 160 V,the primary silicon is further roughened and agglomerated,but the overall distribution is uniform;When the pulse voltage increases to 240 V,the phenomenon of agglomeration and coarsening of primary silicon is weakened,and the uniformity of distribution is improved;When the pulse frequency is small(1 ~ 5Hz),the increase of frequency has no obvious influence on the distribution and morphology of primary silicon.Only when the frequency increases to 10 Hz,the phenomenon of segregation and coarsening will occur;With the increase of pouring temperature and mold preheating temperature,the average size of primary silicon increases gradually;under the same conditions,there is a larger size of primary silicon with a pulsed magnetic field than without pulsed magnetic field;The pulse magnetic field process parameter has no obvious influence on the hardness of Al-20 Si alloy,and the overall hardness tends to be uniform when distributed uniformly.The hardness of the edge is higher than that of the central hardness when there is segregation.3)Al-20 Si functionally graded material was successfully prepared by changing the parameters of pulsed magnetic field.The primary silicon was aggregated at the edge of the sample,and there was no primary silicon in the core.When the pulse voltage changes in the range of 0~150V,with the increase of the pulse voltage,the shape of primary silicon changes from bulk to thick strip,and the average distribution width of primary silicon decreases gradually;When the pulse frequency changes in the range of 1~10Hz,the average distribution width of primary silicon decrease gradually with the increase of pulse frequency;When the pouring temperature have range of 690?~780? or mold temperature have range of 400?~700? changed,with pouring temperature or mold temperature increases,the average width of primary silicon decreases first and then increases,a turning point was 750 or 600 degrees centigrade;Under pulsed magnetic field,the addition of P refined the primary silicon in the alloy,but at the same time inhibited the migration of primary silicon and reduced the average distribution width of primary silicon in Al-20 Si alloy;The hardness of Al-20 Si alloy segregation zone is higher than that of center zone under pulsed magnetic field;The wear resistance of the center and edge was not obviously different when untreated,the wear resistance of the edge was higher than that of thecentral part when combined with magnetic treatment or magnetic field and P treatment.