Bath for pretreating light metals which are susceptible to oxide formation prior to electroless coating - made up of aqueous phosphoric acid

摘要

Prior to electroless coating of light metals, the surfaces of light metals which form oxide layers are pretreated in an aq. bath contg. phosphoric acid contg. 100-550 g/l, esp. 300 g/l +/- 10% acid. The water used is distilled or deionised and the bath is stirred by either a pump or air. The bath temp. is 10-45, esp. 20-25 deg.C and the treatment time is 3-20, esp. 6-7 min. During the process the voltage is slowly increased at rate of 1 volt +/- 40% per 10 sec +/- 40% to an end voltage of 5-25, pref. 10-20 volts. The treatment produces a thin porous layer pref. thinner than 0.5 micron m. and esp. a few atoms thick. The final coating is pref. NiP with SiC and/or PTFE and/or BC and/or Al2O3 dispersed in it. USE/ADVANTAGE - Pretreating Al, Mg, Ti metal or alloy surfaces prior to electroless coating with Ni, Cu, noble metal such as Au. The treatment stages are shorter than in the prior art. There is less of a pollution problem and the bath has a long standing life. The process produces good results in a cheap and simple manner.