Frequently Asked Questions
Aluminium bronzes are copper alloys containing, amongst other additions, up to 14% by weight of aluminium. Nickel aluminium bronzes are a subset aluminium bronzes which also contain nickel and often iron and manganese. Nickel aluminium bronzes are generally stronger than other aluminium bronzes and possess a two phase (duplex) microstructure.
Nickel aluminium bronzes possess an alumina surface oxide that gives good corrosion resistance, however, this oxide can cause inclusions and other flaws during welding, if entrapped in the weld metal. Interpass and preweld cleaning must be employed to avoid this. As with all welding, general surface cleanliness will improve the quality of the weld.
All aluminium and nickel aluminium bronzes undergo metallurgical changes in the HAZ and weld areas following welding which may lead to deleterious effects on the corrosion properties of the component. Depending on the severity of the service conditions, a postweld heat treatment may be advisable.
Techniques for welding Ni-Al bronzes
Gas shielded techniques such as TIG (or gas tungsten arc welding (GTAW)) and MIG (or gas metal arc welding (GMAW)) are the recommended methods for joining these materials. These methods limit the oxidation of the weld pool and, by the action of the arc, disperse surface oxide. TIG and MIG may both be used for the root pass and fill, MIG being generally faster, but of a lower quality. Pulsed MIG welding may give improvements in controllability. Pure argon, pure helium or mixed argon/helium shielding gases are normally used.
Manual metal arc (MMA) (or shielded metal arc (SMA)) welding is also possible but results may be less satisfactory than for gas shielded techniques. Care must be taken not to cause surface oxide and/or slag entrapment.
Matching filler metals are normally selected when welding Ni-Al bronzes. Standards for consumables include: British Standard BS EN ISO 24373:2009 'Welding Consumables - Solid Wires and Rods for Fusion Welding of Copper and Copper Alloys - Classification'; AWS A5.6/A5.6M: 2008 'Specification for Covered Copper and Copper-Alloy Arc Welding Electrodes'; and AWS A5.7/A5.7M: 2007 'Specification for Copper and Copper-Alloy Bare Welding Rods and Electrodes'.