Joining

Q Is it possible to braze leaded brasses such as CW614N (CZ121Pb3)? Are there any problems to look out for ?

A The problem caused by lead is it becomes molten before brazing occurs and wetting of the joint is impaired. To counter this, use plenty of flux and agitate to break up the surface tension of the lead. Use a joint gap of 2 to 5 thousands of an inch and specify a low melting point silver brazing alloy from BSEN 1044: 1999 Brazing Filler Metals. Select alloy Ag103.

Q Can copper nickels be welded directly to steel?

A Yes they can using appropriate 65% nickel-copper consumables to avoid iron dilution effects.

Q Are 90-10 welding consumables available for welding 90-10 copper nickel?

A They are available but 70-30 copper nickel consumables are preferred for welding both the 90-10 and 70-30 alloys due to superior deposition characteristics.

Q Can copper nickels be brazed?

A Yes they can be brazed by all processes. Appropriate silver brazing alloys should be used as phosphorus bearing brazing alloys cause a reaction with nickel to form a brittle phosphide phase.

Q Is post weld heat treatment required when welding copper-nickel alloys?

A Post weld heat treatment is normally unnecessary.

Q A brass water fitting in dezincification resistant brass has been brazed. Should it be re-heat treated?

A Yes, heat to 500 to 525^oC, hold for two hours and slow cool, to ensure an all alpha structure.

Q Are weld repairs permissible on Class 1 and Class 2 nickel aluminium bronze forgings produced to Def Stan 02-833?

A No, the rectification of defects by welding is not permitted on Class 1 and Class 2 (high integrity) forgings.

Q I understand that welding may have an effect on the corrosion resistance of the nickel aluminium bronzes. If so what treatment may be carried out to reduce this effect?

A Yes, the heating effect of welding has the effect of producing a phase change in the alloy which on cooling leads to the formation of the corrodable martensitic beta phase. Annealing at 675^oC for 2 to 6 hours after welding restores the pre weld structure and relieves stress. It is very effective in resisting subsequent corrosion.

Q We have produced a number of tin bronze castings which show extensive porosity. The result of this is that the castings have failed a pressure test and show fluid leakage. It has been suggested that weld repairs may be a solution. Is this so?

A No, the usual solution for treating porosity in castings is by impregnation where the casting is placed in a vacuum and the porosity is filled with either a polyester or epoxy resin. This process is approved for military applications (except Class 1 castings).

Q Are lead containing solders being phased out for all engineering applications?

A Lead is NOT being categorically phased out but the use of lead (and cadmium) is being increasingly recognised as being undesirable both in terms of the long term environmental impact and recyclability of products. The End of Life Vehicles (ELV) Directive (2000/53/EC), the RoHS Regulations (2002/95/EC) and WEE Directive (2002/96/EC) prevent the use of certain hazardous substances including lead (and cadmium) containing materials. The use of leaded solder in potable water systems has also been prohibited in Europe and in many countries worldwide.

Q We have cast a bush weighing 200 kg, in G1 Gunmetal( 88Cu,10Sn,2Zn). At three places there is a hot tear at the point where the body of the bush joins the flange, on the inner diameter. We have made a "V" shaped groove to prepare for welding, but our customer says that he will only permit the repair if the BS 1400 G1 standard allows it. There is no sign of any defect after the groove has been made, i.e. it is only a surface defect. Can you give me an idea of what repairs are permitted under the standard, any conditions attached?

A From BS 1400. Weld repair is only permitted with the written approval of the purchaser and his acceptance of the proposed method of reclamation repair. Similar wording in EN1982 with the additional comment that, if corrosion resistance is a concern, then a post weld heat treatment should be carried out.