Study Of Ageing Behavior Of Aluminium Matrix Composites

In this study , Mullitef/Al-4.5Cu and Mullitef/Al-Mg-Si composites have been produced by squeeze casting . the effect of the retained deformation made after ice-water quenched with 0, 12.5, 25 or 34.4% on the ageing hardening behavior of Mullitef/Al-4.5Cu composites and Al-4.5Cu alloy have been investigated by means of hardness measurement (HB). , The ageing precipitation sequence of Mullite/Al-4.5Cu composite and Al-4.5Cu alloy with retained deformation have been respectively detected by differential scanning calorimetry (DSC) , The morpholojies of the precipitates have also been observed by scanning electron microscope and transmission electron microscope(TEM) and energy dispersive X-ray spectroscopy (EDX). The ageing behavior of Mullitef/Al-Mg-Si and their base alloys with balanced (Mg/Si=2) ratio of Mg/Si , excess silicon (Mg/Si<2)and excess Mg (Mg/Si>2) compositions have also been studied through the same way .The retained deformation forced on Mullite/Al-4.5Cu composite and Al-4.5Cu alloy has also effectively strengthened the materials .The tetained deformation considerably accelerates the ageing response of Al-4.5Cu alloy and the effect of precipitation acceleration is further promoted with increasing deformation degree. Moreover , the age-precipitation progress of the testing composite is further accelerated when there exit both of the fibre and the deformation . The GP zone formation is , however , suppressed due to the introduce of retained deformation and /or short mullite fibres.It is shown that wether the composites or the base alloys, they both have the similian age-hardening curves and the same precipitation procedure. The ageing-hardness of Al-Mg-Si alloys are increased when synthenized with the mullite short fibres , which to some content accelates the age-hardening progress of Al-Mg-Si alloys . but the fibre dosent suppress the formation of GP zones. Temperature affected the ageing hardening behavior of the Mullitef/Al-Mg-Si composites and their matrix alloys in the same way . The chemical composition has strength effect on the ageing hardening behavior of Mullitep/Al-Mg-Si composites and their monolithic alloys . The excess of Mg or Si each obviously accelerates theage-hardening progress of Al-Mg-Si base alloys . What' s more , the ageing peaks of the composites and base alloys are obviously advanced .