BAg30CuZnSn退火过程中组织性能演变

Evolution of Microstructure and Properties of BAg30CuZnSn During Annealing

Ag基钎料由于具有适宜的熔化温度范围、良好的流动性、润湿性及优良的力学性能而受到广泛关注。其中,带状银钎料更因其能够预置工件填缝、便于实现自动化、提升焊接效率、节能节材等优点,成为近些年来市场广泛采用的钎料。但要制成表面洁净、氧化夹杂少的带状钎料,轧制工艺是关键。目前带状银钎料在轧制过程中,轧制道次繁琐,杂质易引入,这些杂质的引入影响了产品的外观,更重要是使得钎料的润湿性和流动性都会有较大波动,最终导致焊接接头的质量下降。为获得良好的钎料表面质量,降低杂质引入概率,轧制前均需选择合适的退火工艺以优化钎料组织,从而减少轧制次数,提升质量的同时提高生产效率。本工作采用金相显微镜、扫描电镜(SEM)、能谱分析(EDS)、显微硬度等多种分析手段系统研究了BAg30CuZnSn钎料在不同退火温度、时间下组织和硬度的变化规律,研究结果表明BAg30CuZnSn微观组织和硬度在不同退火温度、保温时间下差异较大。随着退火温度的升高,富银相基体中的Ag不断向网状相中扩散,Ag含量不断降低,整体均匀性增加;铜从富铜相中向基体相中迁移。当温度超过500℃,晶粒粗化,出现大量的树枝晶,在枝晶末端Sn和Ag不断富集,并沿着晶轴方向不断扩展。当500℃退火保温90 min,能够得到均匀细小的晶粒组织,钎料硬度也较大幅降低,可以实现轧制单道次最大9 mm的压下量而不会发生轧裂,与传统的550℃退火120 min后分三道次轧制9 mm压下量相比,在退火温度及退火时间方面有明显的优化。

Ag-based brazing filler metal has been used widely due to its suitable melting temperature range,good fluidity,wettability and excellent me-chanical properties.Ribbon-shaped silver solder has been popular in recent years because of its ability to pre-set the workpiece to fill the gap,facilitate automation,improve welding efficiency,and save energy and materials.However,the rolling process is the key to make ribbonshaped brazing filler metal with clean surface and less oxidized inclusions.At present,the impurities introduced by the cumbersome rolling pass affect the appearance of the product,but more importantly,the wettability and fluidity of the solder will fluctuate greatly,which will eventually lead to the decrease of the brazing joint quality.In order to obtain good surface quality of brazing metal and reduce the probability of impurity introduction,appropriate annealing process should be selected before rolling to optimize the structure of brazing metal,so as to reduce rolling times,improve quality and improve production efficiency.In this work,the changes of microstructure and hardness of BAg30CuZnSn solder under different annealing temperatures and times were studied by many analytical methods,such as metallographic microscope,scanning electron microscope(SEM),energy spectrum analysis(EDS),microhardness tester and so on.The results showed that the microstructure and hardness of BAg30CuZnSn varied greatly under different annealing temperatures and holding times.With the increment of the annealing temperature,the Ag in the silver-rich phase matrix continuously diffused into the network phase,with Ag content decreasing gradually and the overall uniformity increasing.When the temperature exceeded 500℃,the crystal grains became coarse and a large number of dendrites appeared.Sn and Ag continuously enriched at the ends of the dendrites and expanded along the crystal axis.When annealing at 500℃for 90 minutes,a uniform and fine grain structure could be obtained,and the hardness of the solder reduced greatly.The maximum reduction of 9 mm in a single rolling pass could be achieved without rolling cracks,which was different from the traditional annealing at 550℃for 120 min.