Research On Purification Of Recycled Aluminum Alloy A356

Abstract:Aluminum alloy A356are widely used for automotive, aerospace and other industries because of its improved mechanical properties, excellent casting properties and processing performance.Iron is considered the most harmful impurity in the aluminum alloy, which comes from the bauxite ores and alloying elements.Therefore,the development of a low-cost and efficient renewable scrap processing technology has important significance for the sustainable development of China’s aluminum resources.In this thesis,The effects of addition of B2O3, Al-B,Al-Mn,Mn/B and mechanical vibration on the solidification microstructures,mechanical properties and the impurity iron in recycled aluminium alloy A356have been investigated by modem analysis equipments such as optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction(XRD),direct reading spectrometer and so on.The feasibility of using boron compound to remove iron impurity was demonstrated by the thermodynamic and kinetic calculation. Furthermore, the removal of iron impurity mechanisms of recycled aluminum alloy A356was discussed. The main conclusions can be summarized as follows:(1) The impurity iron content of recycled aluminum alloy A356reduces with increasing B2O3addition and holding time.The optimal addition of B2O3is0.6%and optimal holding time is90min, with Fe decrease from1.32%to0.97%, its removal ratio is26.5%.(2) The microstructure of recycled aluminum alloy A356is fined and the iron content decreases with increasing Al-3B addition, and the iron content is reduced from0.96%to0.68%by addition of3%Al-3B. The tensile strength and elongation are improved to some extent; they are increased by20.5%and38.6%, respectively, compared with that under no purification treatment.(3) Mechanical vibration can make the bulky dendrite broken and the primary phase a is translated to isometric as well as the secondary dendrite arm space of alloy decreases during the process of solidification of recycled aluminum alloy A356, the majority of the morphology of P phase forms long needle-like into short rod-like which uniformly distributed in the grain boundary through application of mechanical vibration in the process of solidification with increase of vibration frequency. The tensile strength and elongation of recycled aluminum alloy A356with addition of3%Al-3B are171MPa and4.74%respectively, when the vibration frequency is40Hz, the value of tensile strength and elongation of recycled casting aluminum alloy is increased by9.6%and34.6%respectively compared with that without vibration(4) The impurities iron content of recycled aluminum alloy A356reduces with increase of Mn and B combined addition, the ratio of iron removal of recycled aluminum alloy A356is the most obvious, so that it reachs55.2%if the Mn/Fe ratio is1.2, the iron content reduces from0.96%to0.43%.The optimized mechanical properties can be obtained with Mn/Fe=1.2and the optimal addition of3%Al-3B,whose ultimate tensile strength and elongation are177MPa and10.92%,respectively, when frequency is30Hz.