Study On Fabrication And Properties Of In Situ ZA27 Alloy Matrix Composites

In this paper,the ZA27 alloy was choosed as matrix material.Sip/ZA27 composites were fabricated by mixing pure zinc melt with aluminum-silicon alloy melt,which was used as the carrier of silicon.Based on a constant mixing process,the influence of modification of P+RE and K₂ZrF₆ on the microstructure and properties of Sip/ZA27 composites were stuied.According to the mechanical properties,wear properties and thermal expansion of composites,the mechanism of reinforcements has been analyzed.The average size of primary silicon can be reduced from 100μm to 25μm by superheating the hyper-eutectic Al-20wt%Si alloy to 850℃and keeping for 30min, and to 10μm by adding 0.1wt%P element.The addition of RE element is not useful to the primary silicon appearance,while it is useful to the eutectic silicon.After the modification of P+RE,the hyper-eutectic Al-20wt%Si alloy melt was mixed with the pure zinc melt.As the pouring temperature is higher than 700℃,the series of Sip/ZA27 composites with fine and well-distributed silicon particles can be obtained.After remelting the Al-20wt%Si alloy and adding K₂ZrF₆ powder into the melt, composite melts with Si and Al₃Zr phases can be obtained after the chemical reaction. Via the same mixing process of Sip/ZA27,the composite melt can be mixed with pure zinc melt.The(Al₃Zr+Sip)/ZA27 composites with silicon particles and Al₃Zr strips can be obtained.The fine dentrite of aluminum-zinc matix also can be observed in respect that the Zr element can hinder the growth of primaryαphase.The tensile strength of composites at the room temperature are higher than that of ZA27 alloy in respect that the adding of silicon.The tensile strength increases gradually while the elongation comes down rapidly along with increasing silicon volume fraction.The highest tensile strength can be obtained as the silicon content is 9vol%.As it is higher than this value,the tensile strength will decrease gradually along with increasing silicon volume fraction.It is because the ebbing effect surpasses the strengthening effect as the content of silicon phase is over 9vol%.The variation of the tensile strength and the elongation of(Al₃Zr+Sip)/ZA27 composites is consistent with those of Sip/ZA27 composite.The tensile strength of(Al₃Zr+Sip)/ZA27 is slightly lower than that of Sip/ZA27 composites with the same Si content,while the elongation is higher due to the addition of zirconium salt.The hardness of composites increases gradually along with the increasing of silicon volume fraction.The hardness is 152HBS as the silicon volume fraction is 12vol%,which is 29%higher than that of ZA27 alloy.According to the appearance of Al₃Zr,the hardness of(Al₃Zr+Sip)/ZA27 is slightly higher than that of Sip/ZA27 composites.The wear performance of composite is better than that of the matrix alloy. However,the wear performance does not increase linearly with the increasing of the volume fracture of reinforcement phase.When the silicon content is 12vol%or 14vol%,the high temperature(100℃) wear performance enhances greatly,which is almost the same as the ambient wear performance.The thermal expansion of composites at the range of 20-300℃indicates that the reinfocement phase could confine the thermal expansion of composite due to the difference of thermal expansion coefficients of the reinforcements and the alloy matrix.