There are two types of beryllium copper alloys. High strength beryllium copper alloys (Alloys 165, 15, 190, 290) have higher strength than any copper alloy and are widely used in electrical connectors, switches and springs. The electrical and thermal conductivity of this high-strength alloy is about 20% of that of pure copper; high-conductivity beryllium copper alloys (alloys 3.10 and 174) have lower strength, and their electrical conductivity is about 50% of pure copper, used for power connectors and relays. High strength beryllium copper alloys are easier to resistance weld due to their lower electrical conductivity (or higher resistivity).
Beryllium copper obtains its high strength after heat treatment, and both beryllium copper alloys can be supplied in pre-heated or heat-treated state. Welding operations should generally be supplied in a heat-treated condition. The welding operation should generally be carried out after heat treatment. In resistance welding of beryllium copper, the heat affected zone is usually very small, and it is not required to have a beryllium copper workpiece for heat treatment after welding. Alloy M25 is a free-cutting beryllium copper rod product. Since this alloy contains lead, it is not suitable for resistance welding.
Resistance spot welding
Beryllium copper has lower resistivity, higher thermal conductivity and coefficient of expansion than steel. Overall, beryllium copper has the same or higher strength than steel. When using resistance spot welding (RSW) beryllium copper itself or beryllium copper and other alloys, use higher welding current, (15%), lower voltage (75%) and shorter welding time (50%) . Beryllium copper withstands higher welding pressures than other copper alloys, but problems can also be caused by pressures that are too low.
To obtain consistent results in copper alloys, welding equipment must be able to precisely control time and current, and AC welding equipment is preferred due to its lower electrode temperature and low cost. Welding times of 4-8 cycles produced better results. When welding metals with similar expansion coefficients, tilt welding and overcurrent welding can control the expansion of the metal to limit the hidden danger of welding cracks. Beryllium copper and other copper alloys are welded without tilting and overcurrent welding. If inclined welding and overcurrent welding are used, the number of times depends on the thickness of the workpiece.
In resistance spot welding beryllium copper and steel, or other high resistance alloys, better thermal balance can be obtained by using electrodes with smaller contact surfaces on the beryllium copper side. The electrode material in contact with beryllium copper should have a higher conductivity than the workpiece, a RWMA2 group grade electrode is suitable. Refractory metal electrodes (tungsten and molybdenum) have very high melting points. There is no tendency to stick to beryllium copper. 13 and 14 pole electrodes are also available. The advantage of refractory metals is their long service life. However, due to the hardness of such alloys, surface damage may be possible. Water-cooled electrodes will help control tip temperature and prolong electrode life. However, when welding very thin sections of beryllium copper, the use of water-cooled electrodes can result in quenching of the metal.
If the thickness difference between the beryllium copper and the high resistivity alloy is greater than 5, projection welding should be used due to the lack of practical thermal balance.