Effect Of Alloying Elements On The Wettability,Microstructures And Properties Of Cu/ATO Electric Contact Materials

Copper-base electric contact material is one of the important development directions of contact material silver saving and environmental protection design for low-voltage electrical equipment. The urgency of the demand increases daily with the scarcity of precious metal resources and the rising price of silver. At present, the main problem of copper-base electric contact material design for low-voltage electrical equipment is the wettability between the matrix and second phase has been ignored. The wettability of the matrix and the second phase will affect the degree of densification, oxidation characteristics and contact stability of material.In this paper, the effect of alloying elements on the wettability of Cu/Me O system and the microstructures and properties of copper-base electric contact material have been studied. The effect of alloying elements（Zr、La、Cr、Ag） on Cu/Me O system has been studied through the sessile drop method and the powder wetting method, then we concluded that the above elements could effectively improve the wettability composition range of Cu/Me O system. On the basis of studying the change of the microstructures and properties of the composite material after unary alloying, the relation between microstructures and properties of copper-base electric contact material after compound alloying has been studied.The conclusions of wetting test are as follows: The addition of four kinds of alloying elements（Zr, La, Cr, Ag） can effectively reduce the contact angle of Cu/Al₂O₃,and improve the wettability of Cu/Al₂O₃ system. When the content of Zr was 0.7wt.%, the contact angle can be reduced to a minimum of 106.9 degrees; When the addition amount of La element was 0.2wt.%, the contact angle reached 103.1 degrees; the contact angle gradually decreases with the increase content of Ag and Cr. When the content of Cr and Ag were 1.6wt.%, the contact angle were 110 degrees and 108 degrees respectively. In the powder sintering experiment, the combination of Cu particles and ATO particles was poor; the Cu Zr and Cu La particles can be combined with the ATO particles, and the wettability was improved.The OM and SEM of alloying copper matrix composites showed that La, Cr, Ag could make the Cu/ATO composite grain refinement; With the increase of the element content, the distribution of La and Zr elements changed with a tendency toward the grain boundaries gradually, while the Cr and Ag elements were distributed evenly in the Cu/ATO composite without segregation phenomenon.Based on the analysis of the properties of the alloy copper matrix composites, Zr and Cr elements can obviously enhance the hardness of the composite, while La and Ag elements has less impact on it. When the content of Zr and La elements were 0.1wt.% and 0.2wt.%, the hardness of the composites reached the maximum value with 126.4HV0.1 and 113.8HV0.1 respectively; With the increase content of Ag and Cr, the hardness of the composites increased, when the content of Cr and Ag was 1.6wt.%, the hardness values of the composites were 129.5HV0.1 and 114.3HV0.1. The addition of Cr and Ag element had little effect on the electrical conductivity of Cu/ATO composites, while the Zr element had a serious damage on it. The addition of Zr, Cr and Ag showed a linear relationship with the decrease of conductivity, and the conductivity decreased by 9.38%IACS, 1.49%IACS, 0.53%IACS, respectively, which caused by the addition of 0.1wt.% alloy element. With the addition of La element, the conductivity of the material decreased first slowly and then rapidly.SEM and TEM on microstructures of copper-base electric contact material after compound alloying showed that Cr, Ag elements equally distributed. Zr element was easy to combine with O and formed oxides. La element might be combined with ATO and formed a new compound. The results of tensile test implied that the bulk density and tensile strength would decrease and the hardness would increase with the increase of La content. The tensile strength, hardness and elongation would increase with the increase of Cr content. Electrical performance test showed that La, Cr, Ag elements would have a bad effect on the electrical conductivity but instead reduce the contact resistance of copper-base electric contact material.