Brazing Alloys

 Select filler metal for a brazed joint depends on five main points:  properties of the filler metal  joint design  service requirements  base metal composition cost and availability 1.Properties. Melting point or melting range determines whether the material flows all at once or over a range of temperatures. Fluidity, poor or good fit up of the braze joint determines if the job needs sluggish or rapid-flowing filler. Knowing the fluidity of the filler metal lets the technician prescribe proper joint clearance. Joint remelt temperature. Filler material alloys with the base material at rates depending on the compositions of both materials and temperature. This interaction determines the composition and the melting temperature of the brazed joint, the temperature at which it will fail by fusion. Vapor pressure. In vacuum brazing the filler metal should have a vapor pressure lower than the vacuum pressure to prevent out gassing of filler metal elements. Such out gassing results in a braze

The brazing properties of copper and copper alloys mainly depend on the following factors: 1. The stability of the oxide formed on the surface. 2. The influence of brazing heating process on material properties. 3. The sensitivity of the material to stress cracking. Two oxides of Cu2O and CuO may be formed on the surface of pure copper. The copper surface is covered by Cu2O at room temperature; the oxide scale at high temperature is divided into two layers, the outer layer is CuO, and the inner layer is Cu2O. Copper oxides are easy to remove, so the brazing properties of pure copper are very good. Oxygen copper is copper refined by fire and electrolytic toughening grade copper. It contains oxygen with a mass fraction of 0.02% to 0.1%. Oxygen exists in the form of copper oxide and forms a eutectic structure with copper. This eutectic structure is distributed in the copper matrix in the form of small balls. If aerobic copper is brazed in a reducing atmosphere containing hydrogen, hydroge

Another thing to consider is not just to consider the influence of temperature and time on the quality of welded joints. As the temperature of the welding alloy increases, the alloying and wettability of the filler will increase. Under normal circumstances, the welding temperature must be selected as a filler metal higher than the melting point. However, there are several factors that affect the temperature selection of the welding design.  The best welding temperature must take into account: (1) the lowest possible welding temperature, (2) minimize the influence of thermal effects on the assembly, (3) keep the interaction of the filler/base metal to a minimum, and (4) ) Maximize the use of jigs or fixtures. In some cases, choose a higher welding temperature to accommodate other factors in the design (such as allowing the use of different filler metals, or controlled metallurgical effects, or adequate removal of surface contamination). Time is an important factor for welding joints, bu

Soldering iron brazing is used for soft soldering of small simple or thin parts. Wave soldering is used for the assembly and soldering of large quantities of printed circuit boards and electronic components. When welding, the molten solder at about 250°C passes through the narrow seam to form a wave crest under the pressure of the pump, and the workpiece is welded through the wave crest. This method has high productivity and can realize automated production on the assembly line. Flame brazing uses a flame of combustible gas mixed with oxygen or compressed air as a heat source for welding. The flame brazing equipment is simple and easy to operate. According to the shape of the workpiece, multiple flames can be heated and welded at the same time. This method is suitable for welding small and medium parts such as bicycle racks and aluminum kettle spouts. Dip brazing involves immersing a part or whole of the workpiece in a solder bath covered with flux or a salt bath with only molten salt