Brass can be welded (to brass), however, it is generally not recommended because it contains zinc which affects the porosity of the weld and releases harmful zinc oxide fumes.
A high degree of skill is needed to avoid excessive volatilization of zinc. Two practical methods are to preheat thick sections and reduce the welding current.
Low zinc brasses have better weldability than high zinc brasses. TIG welding with a zinc-free filler rod is the most popular way of welding brass.
Low and high brasses are more difficult to weld than copper, because brass contains copper and zinc. The chief difficulty in welding brass is the volatilization or loss of zinc due to the fact that the melting point of zinc (420°C) is lower than that of brass (830-960°C).
Loss of zinc during welding is indicated by heavy irritating fumes and a white deposit upon the surface of work around the weld. Loss of zinc causes the following:
- Destroys the proportions of the metals in brass.
- Causes blowholes or porosity in the weld, resulting in reduced strength
The loss of zinc can be prevented by using an oxidizing flame when gas welding. This will form a skin of zinc oxide on the surface of the molten metal, thereby preventing volatilization of molten zinc.
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Ensure there is adequate ventilation
While welding brass, the welder must make sure that they have excellent ventilation conditions and not breathe zinc dust and zinc oxide fumes.
The welder should wear a respirator/PAPR and have a fume extractor to help remove the harmful zinc fumes from the work area.
Which processes can be used for welding brass
Leaded brasses are considered basically unsuitable for electric welding because the lead promotes weld cracking. The oxyacetylene process can be used but high strength joints are generally not obtainable. Low and high brasses, with little or no lead, are commonly welded with TIG, MIG, stick and oxy-acetylene.
TIG Welding brass
Brass up to 9 mm thick can be welded by TIG process. However, this process is most commonly used particularly for light gauges of metal. Thicknesses above 1.5 mm need filler metal. A zinc-free filler metal is recommended. Preheat is not ordinarily used until the base metal is thick. Preheat temperatures in this case range from 94 to 316°C.
Argon and helium are used for least conductive and more conductive alloys respectively. In order to reduce zinc fumes, helium and helium rich mixtures with argon are sometimes used on high zinc brasses. The arc is struck and held on the filler metal rather on the base metal, to help reduce zinc loss and fuming.
Silicon in the filler rod helps decrease zinc fumes.
Filler material for low zinc brasses:
- 93.5% min Cu + Ag
- 4 to 6% Sn
- 0.10 to 0.35% P
Filler material for high zinc brasses:
- 94% min Cu + Ag
- 2.8 to 4% Si
- 1.5% Zn
- 1.5% Sn
- 1.5% Mn
- 0.5% Fe.
MIG Welding brass
MIG welding low zinc brasses
MIG welding is preferred for joining heavier gauges of low-zinc brasses. Silicon bronze or phosphor bronze filler metals are used.
Silicon bronze filler rod contains:
- 2.8-4.0% Si
- 1.5% Sn
- 1.5% Mn
- 0.5% Fe
- Balance Cu + Ag.
A phosphor bronze filler rod contains:
- 7.5-9.0% Sn
- 0.05-0.35%
- Balance Cu + Ag.
A phosphor bronze filler metal gives a good colour match but the silicon bronze deposits will flow more readily at lower current levels. A preheat of 94 to 316°C will reduce current requirements.
DCEP is always used. Argon and Argon + helium are used as shielding gases. A 600 single V -groove joint is used with silicon bronze filler rod. If a phosphor bronze electrode wire is used, its sluggish flow characteristics make a 70° V -groove advisable for heavier thicknesses.
MIG welding high zinc brasses
For MIG welding high zinc brasses, copper-silicon or aluminium bronze electrode wires are used. In case of high brasses, zinc fumes arc more severe and the welds have greater porosity and lower strength than in the low zinc brasses.
Moreover, more zinc fuming is noticed with MIG than with TIG process. Preheating is not necessary, however, it helps to limit zinc fuming as lower welding currents are needed after preheating.
Stick welding brass
Low and high zinc brasses can be welded by shielded metal arc process using phosphor bronze or aluminium bronze covered electrodes. Aluminium bronze electrodes are used where high tensile strength, high fatigue strength and corrosion resistance are required. Phosphor bronze electrodes are preferred for low-zinc brasses.
Welding is restricted to flat position only. Wide grooves are used to obtain proper penetration and to avoid slag inclusions. Preheating may be carried out to get adequate penetration. Low brasses are readily weldable at preheat and interpass temperature of from 205 to 260°C and this temperature for high brasses is from 260 to 371°C. A backing strip of copper should be used. DCEP may be used.
Oxy-acetylene welding brass
Generally, an oxidising flame is employed for gas welding of brasses. A neutral flame is first formed on a test piece. The zinc oxide fumes start coming up.
At this stage the amount of acetylene is gradually reduced till the fumes are completely stopped and a visible white bright thin skin of zinc oxide forms on the molten metal. This film prevents the further volatilization of zinc. This is the correct flame for gas welding brass.
Silicon bronze filler rod of the following composition may be used to have excellent corrosion resistance of welds:
- 94% Min Cu + Ag
- 2.8-4.0% Si
- 1.5% Zn
- 1.5% Sn
- 1.5% Mn
- 0.5% Fe.
Finally, a few extra tips for oxy-acetylene brass:
- Boric acid flux is employed.
- Carbon plate is used as a backing material.
- Forehand technique is generally recommended
- For welding high brasses, filler rods of the same composition as the base metal are used.