The Investigation On Cuw/Al Diffusion Solution Layers

As the development of science and technology,it has increasingly become the first concern of materials that we should cut cost,improve the market competitiveness.CuW/CuCr integrated material has become the predominant material in self-type contacts as a high and an ultra-high voltage switch,whereas its development is restricted,which is due to the shortage of copper resources and high cost.Therefore,it is urgent for us to prepare CuW/Al integrated material to meet the demands of the development of material science and projects,in the trend of "saving copper with aluminium".The CuW/Al diffusion-solution layer（DSL）was prepared by the solid-liquid diffusion bonding process.The effects of experimental conditions on the morphology of DSL were studied,the microstructure,morphology and formation of the sub-DSL was further discussed,the formation of interfacial intermetallic compound was quantitatively analyzed,and the formation sequence was discussed as well,the formation mechanism of CuW/Al DSL was revealed,the alloy element for interface microalloying was choosed by thermodynamic calculation on the basis of the gibbs free energy function.The following conclusions were obtained based on the experimental analysis and theoretical calculation:（1）The microstructures of CuW/Al DSL are very similar in different conditions,only the thickness of the DSL varys with the process conditions.The DSL of CuW/Al integrated material mainly consists of grainy DSL,columnar directional DSL,eutectic DSL and acicular DSL.（2）In different condition,CuW/Al interface migrates towards CuW.And the interface mobility increases with holding time at the same temperature.At the same time,the higher temperature,the greater the interface mobility,the growth of the DSL is mainly affected by the interface chemical reaction process.（3）Al₂Cu and A15W are the main intermetallic compound in the DSL,the relative content of Al₂Cu increases,while that of the Al₅W gradually reduced with the increase of the holding time.（4）The formation process of CuW/Al DSL mainly includes diffusion,dissolution and crystallization of the alloy elements in two substrate material.According to the process of the solid/liquid diffused bonding,the formation is divided into three stages:the physical contact of the Al,Cu and W,the thermal activation of Al,Cu and W,the mutual diffusion of the Al,Cu and W and the formation of the diffusion layer dissolved.（5）The hardness of the DSL is obviously higher than that of the CuW and Al aside.The brittle phase of Al₂Cu and Al₅W were formed.The average microhardness of diffusion-solution layer is higher,which is closely related to the distribution,morphology and number of the intermetallic compound.（6）Thermodynamic calculation indicates that:the gibbs free energy of the AlB₁₂ is the lowest than that of the other in Al-X system when the temperature ranges from 950K to 1000K.Moreover,boron exhibits a high grain refinement effect,it is consequently believed that the B is the effective alloying element.