1 Brazing and Braze Welding TSM 233 Unit 4

TSM 233 Metallurgy and Welding Processes What is brazing? Bond materials melts above 840 degrees F. As in soldering the base metals do not melt. Uses capillary action, Often called “hard soldering”. Silver soldering is a form of brazing.

TSM 233 Metallurgy and Welding Processes What is braze welding? A variation of brazing that does not require/use capillary action. A Brazing material melts, forms a “bead”. Since the base metals do not get as hot as when welding, potentially less distortion.

TSM 233 Metallurgy and Welding Processes Why braze or braze weld metals? Similar to soldering, Provides good strength, sometimes as strong as welding Flexible, malleable. Seals, penetrates. Can be used to bond some dissimilar metals Can be easier to fabricate than welding for some applications.

TSM 233 Metallurgy and Welding Processes How does the brazing process join metals together? Forms a bond with the base metal, Similar, but stronger than soldering, as brazing materials generally have higher strength properties. Adhesion – “gluing”, atomic attraction of the brazing material to the base metals. As with soldering, the brazing material can create “capillary action”, readily flowing between the surfaces of the base metals. Therefore, very good for sealing joints. AWS designates “B” for Brazing, usually a wire, “RB” as a Brazing Rod.

TSM 233 Metallurgy and Welding Processes What types of metals can be brazed? Most metals can be brazed, common applications: Aluminum, Magnesium, Cu and Copper alloys: brass and bronze Cast iron Carbon steels Stainless steel Nickel alloys Titanium

TSM 233 Metallurgy and Welding Processes Preparing the base metals for brazing and braze welding: Chemical cleaning – flux, match to the brazing rod Mechanical - not as critical as soldering, but often need to grind or wire brush.

TSM 233 Metallurgy and Welding Processes What are types of brazing filler metals? Aluminum Silicon, (BAlSi), 80 – 90% Al, 5 -15% Si, used for aluminum and aluminum alloys, service temperature up to 300 F/149 C, solidus about 1050 F/550 C, liquidus 1100 F/ 600 C. Copper and Copper Zinc (RBCuZn, BCu, BCuP) used for a wide range of metals, including carbon steels and cast iron, RBCuZn, RBCuSi,Brass rods, service temperature up to 500 F/260 C, tensile strength 40 kpsi to 60 kpsi, Nickel can be added up to 10% to increase strength, solidus about 1600 F/880 C, liquidus 1630 F/890 C. Note: Tensile strength of low carbon (mild) steel about 70 kpsi.

TSM 233 Metallurgy and Welding Processes Types of brazing filler metals (cont.) Silver –based alloys Silver brazing, (BAg-1…34),  wide range of uses/metals,  Wide range of silver brazing alloys, including Cadmium, Gold, Copper, and Zinc.  Called “silver soldering”, but technically “silver brazing” is correct.  Very strong joints, depending on the thickness of bond.  inches/0.05 mm – 133kpsi  inches/0.15 mm – 90kpsi  (1/64) inches/ 0.38 mm – 70kpsi  Service temperature 400 F/ 204 C.  Generally, too expensive for braze welding.  Solidus 1100 – 1400 F/ 600 – 800 C, depending on the alloys.  Liquidus 1150 – 1600 F/ 615 – 900 C.

TSM 233 Metallurgy and Welding Processes Types of brazing filler metals (cont.)  Nickel based alloys (BNi), Nickel alloyed with Chromium, Zinc and/or Silicon, used for very low temperature applications, carbon and stainless steels, cobalt, and copper-based alloys, solidus 1600 – 2000 F/ 870 – 1070 C, liquidus 1600 – 2100 F/870 – 1150 C.  Magnesium (BMg), used on for Magnesium brazing, two classes: 1. BMg-1 with about 9% Al, solidus 820 F/43 C, liquidus 1110 F/600 C. 2. BMg-2 with about 12% Al, solidus 770 F/410 C, liquidus 1050 F/566 C.  Gold (BAu), 30 – 82% Au, alloyed with Cu, (BAu-1 thru BAu-4), BAu-5 alloyed with Ni, used for electronic and aerospace technologies, used to braze ferrous, nickel and cobalt alloys, very corrosive resistant, service temperature 800 F.427 C.

TSM 233 Metallurgy and Welding Processes What are the types of brazing fluxes?  Borax and boric acid, (white powder) common for steel and iron  Alkaline bifluoride: stainless, aluminum.  Specialized fluxes for specific applications  AWS Types: FB1 – Al, FB2 – Mg FB3 – Steels, including stainless FB4 – Aluminum Bronze

TSM 233 Metallurgy and Welding Processes What are the basic brazing processes? Determine the type of metal, Select the braze rod and flux. Assess the ability of the metal for brazing. Prepare the metal, clean, clearances especially for brazing., and position. Heat source, tip? Forehand or backhand? Tin or not tin the metal? Cooling, Cleaning.

TSM 233 Metallurgy and Welding Processes Reference: Modern Welding: Chapter 10 “Brazing and Braze Welding”