Research The Modification Of Hypereutectic Al-Si Alloy And Related Ternary Phase Diagrams

Hypereutectic aluminum alloys have high strength, low thermal expansioncoefficient, sufficiently high temperature strength and wear resistance etc., which arewidely used. The microstructure of hypereutectic Al-Si alloy casting under normalconditions, which the primary silicon distributes as thick sections polygonal or starshape and the eutectic silicon distributes as long needle. Alloy substrate is split led tothe serious decrease of the mechanical properties, which need modification treatmentto improve performance of the alloy.Made a comparative study using Al-7P and Al-10RE intermediate alloy tomodify individually or complex on Al-26%Si alloy, found that Al-7P and Al-10REmaster alloys have complementary effects on both refinement primary silicon andeutectic silicon. By adding1.0wt.%Al-7P and1.0wt.%Al-RE intermediate alloysin Al-26%Si alloy at800℃，the hypereutectic Al-Si alloy obtain the smallest crystalsilicon of15.8μm and eutectic silicon arranged in short rods or spherical.In order to study the modification mechanism of rich La, Ce rare earth onhypereutectic Al-Si alloy, using scanning electron microscopy、energy dispersivespectroscopy and X-ray diffraction technology. Measuring the Al-Ce-Si isothermalsection and the Al-La-Si poor lanthanum area isothermal section at800℃.Experimental determination shows that the isothermal section of Al-Si-Ce at800℃exists12three-phase regions: Al-rich L+CeSi2-+Si, Al-rich L+CeSi2-+T, Al-richL+T+Al4Ce, Al4Ce+T+Al3Ce, T+Al3Ce+Al2Ce, T+Al2Ce+AlCe, T+AlCe+CeSi, Ce3Si2+CeSi+Ce5Si4, Ce3Si2+CeSi+AlCe, AlCe+Ce3Si2+Ce-rich L,Ce5Si3+Ce3Si2+Ce-rich L, T+CeSi+CeSi2-. Experimental determination showsthat the Al-Si-La ternary isothermal section of poor La at800℃exists4three-phaseregions Al-rich L+LaSi2-+(Si), Al-rich L+LaSi2-+τ, Al-rich L+τ+Al4La, Al4La+τ+Al3La and3two-phase regions: Al-rich L+LaSi2-, τ+Al4La, τ+Al3La.CeSi2-and LaSi2-rare earth compounds absorbed Al atoms and became thecrystallization nucleus of aluminum alloy leading-Al nucleated and causing thecrystalline silicon phase constitutional super-cooling so that inhibited eutectic silicongrew.