WELDING & CUTTING
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WELDING NON-FERROUS ALLOYS
 
NICKEL AND NICKEL ALLOYS
Nickel and nickel based alloys are used in industrial applications for
  • Corrosion resistance
  • Heat resistance and high temperature properties
  • Cryogenic properties
Preheating is not normally required unless there is a risk of porosity from moisture condensation. PWHT is not usually needed to restore corrosion resistance.
 
Inconel type of deposit is used for obtaining high temperature, high strength joints designed to perform at over 200°C such as on creep resistant chromemolybdenum steels to stainless steels. These types are suitable when welding sections over 25 mm. For welding tool steels requiring toughness under repeated cyclic stress and oxidation resistance upto 1000°C, Hastelloy C type of deposit is regularly used. The drop in strength and hardness as the temperature goes up is very gradual.
 
COPPER AND COPPER ALLOYS
The main features of copper and its alloys
  • Corrosion resistance
  • Electrical and thermal conductivity
In terms of weldability, the alloys have quite different welding characteristics. Copper needs substantial preheat to counteract the high thermal conductivity. But alloys like cupro-nickel can be fusion welded without any preheat, as the thermal conductivity is similar to low carbon steel.
 
Buttering technique should be used to join copper alloys to carbon / stainless steel. This is to take care of the copper migration to the HAZ and precipitation at the grain daries. The buttering, with a pure nickel electrode, can be applied on either the copper or the steel side. The groove has to be filled up a stainless or a bronze type of deposit.
 
The preheating should be 300-500°C when buttering copper or bronze whereas the preheating temperature has to be chosen according to the base material if the buttering is done on the steel side.
 
ALUMINIUM AND ALUMINIUM ALLOYS
The characteristics of aluminium and its alloys that make them amenable to fabrication are enlisted below.
These are
  • Light weight
  • Good corrosion resistance
The filler metals used for welding aluminium alloys are selected considering the following aspects
  • Weldability of the parent metal
  • Minimum mechanical properties of the weld metal
  • Corrosion resistance
Nominally matching filler metals are often employed for non-heat-treatable alloys. However, for unalloyed or low alloyed materials and heat-treatable alloys, non-matching fillers are used to prevent solidification cracking.
 
COBALT ALLOYS
Cobalt alloys are known for excellent wear resistance at high temperatures and the weld metal is used in cutting and shearing operations at temperatures exceeding 600°C. These deposits exhibit high shock resistance, high hardness at elevated temperatures and scaling resistance and can be used in stamping dies, trimming cutters, trimming punches, etc.
 
 
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