Research On Low Melting Point Solder Based On 6xxx Series Aluminum Alloy Brazing

As a heat-treatable strengthening alloy,6xxx series aluminum alloy has excellent weldability and thermal conductivity,and can be used in the heat exchanger industry.Aluminum and its alloy brazing often use Al-Si eutectic brazing filler metal.The brazing temperature must be higher than 600 ?,which not only increases the production cost,but also easily causes the grain growth or over-burning of the base material.This article focuses on the low melting point Al-Si-Cu multi-element aluminum-based brazing filler metal suitable for brazing of 6xxx series aluminum alloys.The microelements Ni and Sr are added to improve the structure and properties of the brazing filler metal to obtain high-quality brazing joints.In this paper,DTA,XRD,SEM,EDS were used to analyze and study the influence of alloying elements(Cu,Ni,Sr)on the properties of filler metals,and the brazing process parameters were optimized,and a five-element method for brazing of 6063 aluminum alloy was obtained.The aluminum-based brazing filler metal(Al-Si-Cu-NiSr)was compared with the traditional Al-Si filler metal.The results of the study are as follows:(1)Cu has little effect on the solid line temperature of Al-6.5Si-?Cu filler metal,however has great effect on the liquidus temperature.With the increase of Cu content,the spreading and wetting ability of the filler metal is improved,and the corrosion resistance is reduced.The 6063 aluminum alloy was brazed with Al-6.5Si-20 Cu filler metal at 570 ? for 10 min,the shear strength of the joint reached 117.7 MPa after solution treatment at 500 °C × 1 h and two-stage aging hardening at 160 °C × 1 h +190 °C × 3 h.(2)The addition of a small amount of Ni reduces the liquidus temperature of the Al-6.5Si-20 Cu filler metal and narrows the melting range;Ni improves the spreading performance and corrosion resistance of the filler metal.When brazing 6063 aluminum alloy with Al-6.5Si-20Cu-2.0Ni brazing filler metal,the shear strength of the joint is150.4 MPa,which is 28.32% higher than that of Al-6.5Si-20 Cu brazing joints.(3)The addition of Sr element can significantly improve the structure and properties of Al-6.5Si-20Cu-1.5Ni filler metal.The addition of Sr element further reduces the melting range of the filler metal alloy,the spreading and wetting ability of the filler metal generally increases first and then decreases.The addition of Sr refines the crystal grains and reduces the corrosion resistance of the filler metal.When the Sr content is 0.08 wt.%,the shear strength of the joint is 172.0 MPa,which is 20.7% and46.7% higher than the shear strength of Al-6.5Si-20Cu-1.5Ni and Al-6.5Si-20 Cu filler metals,respectively,which is 27.8% higher than the traditional Al-10Si-2Mg filler metal.