The Reaction And Structure Evolution At The Interfaces Of Al/Al Alloy-SiC/SiC_ox

The interface is a bridge that can connect the metal matrix and the reinforcements as well as a medium of load transferring in the composites.Moreover,interfacial characteristics play a significant role in the comprehensive properties of the composites.The good interface bonding is beneficial to the strengthening of the matrix,the load transfer and preventing the crack initiation as well as propagation along the interface,etc.However,at the interface of SiC/Al composites,the brittle phase Al₄C₃ which formed from the interface reaction between Al and SiC can reduce the strength,elastic modulus and corrosion resistance of the composites.So,in order to obtain a good interface bonding that connect the reinforcement and matrix,it is important to control the interface reaction between Al and SiC to improve the properties of the composites.In this paper,the interface reaction between molten Al and SiC in high temperature was studied.In order to control the interface reaction and restrain the formation of Al₄C₃,the interface reaction of Al/SiC,Al alloys/SiC and Al/SiC_ox（SiC was oxidized with different oxidation parameters）under different reaction conditions（temperature and time）were studied by the method of impregnation.The effect of reaction temperature and time as well as alloying elements（Si,Cu,and Mg）on the interface reaction of Al/SiC and structure evolution were revealed.The effect of the SiC surface oxidation on the interface reaction of Al/SiC_ox and structure evolution were discussed.The optimized reaction process and oxidation parameters were optimized to provide the theoretical and experimental basis for the preparation of SiC/Al matrix composites.1)It was revealed that the reaction parameters have a significant and important role in controlling the occurrence of the Al/SiC interface reaction.With the increase of reaction temperature and the extension of reaction time,the interface reaction degree of Al/SiC was increased,and the formation of the brittle phase Al₄C₃ increased and grew.The increase of temperature is beneficial to the decomposition of SiC,the increase of atomic diffusion rate and the nucleation of Al₄C₃.Furthermore,the extension of reaction time promoted the further growth of Al₄C₃,until the interface between Al and SiC was fully filled with the large Al₄C₃.2)The effect of alloying elements Si,Cu and Mg on the Al/SiC interface reaction and structure evolution were revealed: The addition of Si significantly inhibited the interface reaction.With the increase of Si content,the inhibitory effect was more significant.When the Si content was 12 wt.%,the interface reaction of Al/SiC could be completely inhibited,and there was no Al₄C₃ formation in the interface.Cu is a surface inactive element,and the addition of Cu can reduce the activity of Al,thus,weakening the Al/SiC interface reaction.Mg is a surface active element,which can react with Al and O at the interface to form MgAl₂O₄,thus,weakening the reaction between Al and SiC and reducing the production of Al₄C₃.In the Al2014 alloy,the combination of Si,Mg,Cu alloying elements reduced the formation of Al₄C₃ and weakened the Al/SiC interface reaction.3)The effect and mechanism of pre-oxidized SiC on the interface reaction and structure evolution of Al/SiC_ox were revealed:i)With the increase of oxidation temperature and time,the thickness of oxidation film formed on the surface of SiC increased gradually,but the oxidation rate decreased.The increase of temperature promoted the diffusion of O,which is beneficial to the oxidation reaction.However,with the extension of time,the initial oxidation layer formed on the surface played an important role in blocking the oxidation of SiC,which led to the decrease of oxidation rate.ii)The oxidation layer of SiO₂ formed on the surface of SiC could react with pure Al and prevented the contact between Al and SiC,then slowed down the interface reaction of Al/SiC.With the increase of the oxidation film,its effect on the inhibition of the Al/SiC_ox interfacial reaction was better,and the thick oxidation film could completely prevent the formation of Al₄C₃.iii)The Mg in Al2014 alloy preferentially reacted with SiO₂ and Al to form MgAl₂O₄,which hindered the direct contact between Al and SiC and weakened the Al/SiC_ox interface reaction.The ratio of Al₄C₃ to MgAl₂O₄ on the interface depended on the thickness of the oxidation film: the thicker film,the more MgAl₂O₄.When the film was thinner,it was easy to be consumed,and the SiC which lost the protection of the oxidation film would react with Al to form Al₄C₃,therefore,Al₄C₃ and MgAl₂O₄ coexisted on the interface.When the oxidation film was thicker,it could effectively protect the surface of SiC,so there was only MgAl₂O₄ on the interface.4)The optimized reaction and oxidation process to prevent the Al/SiC interface reaction and reduce the formation of Al₄C₃ were put forward:i)Al-SiC system: control the reaction conditions within 750℃,and 10 min or 700℃,and 15 min.ii)Al-SiC_ox system: when the oxidation parameter was 1100℃-2h,control the reaction conditions within 700℃,and 30 min;when the oxidation parameter was 1100℃-3h,control the reaction conditions within 750℃,and 30 min.iii)Al2014- system: when the reaction parameter was within 750℃-15 min,the formation of Al₄C₃ was less.iv)Al2014-SiC_ox system: when the oxidation parameter was 1100℃-2h,there was only MgAl₂O₄ formed in the interface with the reaction conditions within 850℃,and 30 min,and no Al₄C₃ was founded.