Al Alloy Solder Of Low Melting Point And Its Preparation And Properties

Until recently,Al-Si solder are widely used in 6061Al Alloy Vacuum Brazing Joints.Because brazing temperature of Al-Si solder is higher than that of 6061 aluminum alloy solidus,the corrosion and grain growth are easily accrued in substrate.Therefore,the heat treatment of 6061 Al alloy is necessary after brazing.In this article,the traditional Al-Si alloys were replaced by Al-Mg-Si-Cu（Y）solders to decrease melting point of solder.Besides,the influence of Cu content on microstructure,mechanical properties of the welding joints and wettability between the brazing filler and substrate were discussed fuller.Furthermore,optimized alloy components was obtained.Results showed that joint defects were easily occurred when the brazing temperature of traditional Al-Si alloys solder at 608℃for 70min in Vacuum brazing process.It should be noted that,with the increasement of Cu content,liquidus temperature of Al-Si-Mg-xCu solder was decreased accordingly.However,while the contents of Cu exceeded 12 wt.%,the liquidus tend to be stabled.In contrast,the melting temperature range became small by increasing Cu contents.When the content of Cu increased,the flow paved area of Al-Si-Mg-xCu solder on66061 Al alloy was increased first,then decreased.In addition,while the Cu content was up to 12 wt.%,the flow paved area reached maximum.It found that Al-Si-Mg-xCu brazing alloy was composed of a-Al,Si,Al2Cu and Al4Cu2Mg8Si7.However,the phase of Al₂Cu growth larger with Cu content,and its phase morphology and distribution in solder was essentially unchanged.It showed that the microstructure of Al-Si-Mg-xCu/6061 Al alloy consist of large amounts ofα-Al and a small amount of pure Si,Al₂Cu and Mg₂Si.After insulation for 70min,the atomic diffusion between the solder and substrate is relatively higher,and the elements was distributed uniformly in weld joint.Hardness of weld joint is unchanged because of the uniform diffusion of Cu and Si elements.We also found that tensile strength of Al-Si-Mg-xCu/6061 Al alloy joints firstly increased and then decreased with Cu addition increase in the range from 82MPa to 93Mpa.And while the Cu addition was up to 12 wt.%,the Tensile strength reached maximum value of 93Mpa.It found that 0.5wt.%of Y has no influence on solid-liquid line of Al-Si-Mg-xCu-0.5 Y（x=10,12）solder,and the melting temperature of Al-Si-Mg-12 Cu-0.5 Y in the range from 516.6℃to 550.7℃.Interestingly,Rare-earth Y can effective Refined the microstructure of Al-Si-Mg-xCu-0.5 Y（x=10,12）solder,which will helpful to enhance the joint strength.And with the increasement of Y contents,the solder surface tension reduced and older area of spread increased,maximum spreading area of 372 mm² of Al-Si-Mg-12Cu-0.5Y solder was obtained consequently.This finding was important that,RE was not only improving the microstructure of the solders,but it was also improving the brazing connections,which will helpful to improve the mechanical properties of weld materials.We believed that the results mentioned above will provide a new method to eliminate the heat-treatment step after brazing on 6061 Al alloy,and it will has a broad application prospect in the field of welding manufacturing.