Effects Of Ca Element On The Microstructure And Mechanical Properties Of Al-Cu Alloys

Al-Cu alloy is widely used in aerospace,construction and equipment manufacturing and other fields due to its excellent mechanical properties and wear resistance.At present,scholars have carried out extensive research on Al-Cu alloys with Cu content less than 5wt.%,but the large solidification interval of Al-Cu alloys led to hot tearing,and the poor casting properties were limited the development for it.The content of Cu has an important effect on the properties of Al-Cu alloy,an increase of Cu content in the alloy can effectively improve the hot tearing resistance and casting properties of the alloy.It is worth noting that the hypereutectic Al-Cu alloy is a suitable candidate for the multiphase composites that the reinforced phases（θ-Al₂Cu phase）embedded in a flexible matrix.Compared with traditional metal materials,intermetallic material has wide application prospects in industrial production due to their unique advantages,and has become an important direction in the research of new metal materials.In addition,Ca element accumulates continuously in recycled aluminum,and its removal will cause environmental pollution and material loss.With the vigorous development of recycled aluminum industry,which the green and efficient treatment of Ca element in aluminum alloy is worth further research as a comprehensive.Therefore,the effect of Ca element on microstructure and properties of Al-Cu alloys with high Cu content was systematically studied in this paper.The main contents were as follows:（1）In this study,the effects of Ca element on the microstructure of primaryα-Al and eutectic（θ-Al₂Cu+α-Al）in Al-10Cu alloy was investigated.It was found that the addition of Ca could effectively refine the primaryα-Al grain due to the constitutional supercooling caused by the enrichment of Ca atoms at the front of liquid-solid interface during the solidification process.Simultaneously,the increase of the supercooling degree inhibited the formation of the divorced eutectic phenomenon,and the eutectic structure was further improved with the decreasing of lamellar spacing of eutectic structure.Consequently,the strength and ductility of the Ca-added Al-10Cu alloys were increased.Compared with the unmodified Al-10Cu alloy,the tensile strength of Al-10Cu-0.4%Ca was increased to 237 MPa.In addition,the fracture elongation increased from 1.2%to 4.3%,which was 3.6 times than that of the unmodified Al-10Cu alloy.However,the mechanical properties deteriorated sharply due to the splitting effect of Ca-rich compounds on the matrix when the excessive calcium was added.（2）Hypereutectic Al-40Cu alloys with different Ca contents were prepared by melting casting process.The effects of Ca elements on the primaryθ-Al₂Cu phase and eutectic structure（θ-Al₂Cu+α-Al）in hypereutectic Al-40Cu alloys were investigated.The results showed that the Ca can significantly improve the size and morphology of primaryθ-Al₂Cu phase,the modification mechanism of Ca elements on the primaryθ-Al₂Cu phase is adsorption poisoning mechanism.During the solidification process,Ca atoms are enriched at the front of the solid-liquid interface and form calcium-rich layers around the primaryθ-Al₂Cu grains,which prevents the accumulation of solute atoms and thus limits the radial and axial growth of the primaryθ-Al₂Cu phase.The decrease of lamellar spacing in eutectic microstructure was mainly due to the increase in undercooling with the addition of Ca element,which the lamellar spacing decreases from 0.49μm to 0.32μm.（3）The effect of Ca addition on mechanical properties of hypereutectic Al-40Cu alloy was investigated.The results showed that the addition of Ca reduced the hardness of the alloy,which is caused by the decrease of the primaryθ-Al₂Cu phase size.The addition of Ca element can significantly improve the compressive strength and tensile strength of the alloy at room temperature.When the content of Ca element is 0.6 wt.%,the tensile strength and compressive strength of the alloy increase from 80.78MPa and 378.89MPa to 144.72MPa and 518.44MPa,which were 79.13%and 36.83 larger than those of Al-40Cu alloy.（4）The effect of Ca element on the wear resistance of hypereutectic Al-40Cu alloy was studied.The addition of Ca element could improve the wear resistance of the alloy,among which the wear resistance of Al-40Cu-0.6Ca alloy was optimal.Under 15N,20N and 25N loading conditions,the volume wear of Al-40Cu-0.6Ca alloy compared with Al-40Cu alloy decreased to 0.025mm³,0.090mm³ and 0.140mm³ with the increase of load,and the specific wear rate decreases by 48.8%,24.5%and 29.3%,respectively.The wear mechanism is mainly abrasive wear and stripping wear.