Introduction
With the use of lead-free solder, the common solderpot construction materials will show a corrosive wear in due time after being exposed to the lead-free solder. The friction on pump and nozzle parts caused by the solder flow gives on these parts a more excessive wear. These materials, which could often well be used for tin-lead solders, are now showing wear, which is mainly a result of the change in solder alloy and the use of higher solder temperatures. An investigation was done to search for materials that are more resistant to this wear, so that the lifetime of these parts will be substantially extended, so that they do not need to be exchanged due to wear.
Test Conditions
A test in a running solderpot at a temperature of 400°C was chosen, which is well above the common process temperatures for lead-free wave soldering. As solder the most commonly applied lead-free SnAgCu alloy was used.
Materials tested
Stainless steel AISI 301, 304, 316 and 321. Also Hastelloy, SST316-Ti alloy, Nicofer6023 H, Nicofer 6025 HT and some cast iron samples were tested. On non-of these samples a coating was applied. Coatings tested were heat resistant alkyd based paint and galvanic wear resistant coatings. Also vapor deposited coatings were tested like CrN and TiAlN. Finally diffusing coatings like the QPQ Nitride and a CrxCy coating were compared in this test. The base material for these coatings was low carbon construction steel.
Test results
From all materials and coatings that were tested only cast iron, and steel coated with a diffused CrxCy layer, did pass the test without showing any wear after more than 6000 hours of testing.
One of the failing samples
Sample that passed the test
Cross Section of passed sample
Conclusion
The best protection was established with a ceramic CrxCy layer with a layer thickness of 3 - 30 micron and a hardness of about 2000 Vickers. This layer does not only protect against wear, but also adhesion of solder or dross is much lower due to the low friction coefficient of this layer. These wear resistant parts are replacements for the standard parts. This includes pump and nozzle parts.