Pickling aluminium or its alloys before coating with adhesive - using hot, strong sulphuric acid soln. to dissolve oxide skin

摘要

A pickling process for aluminium and its alloys for improving the bond between the aluminium and adhesive castings, the pickling soln. consisting of pure sulphuric acid used for anodic polarisation. The novelty is the use of higher sulphur(sic) concns. and temps. with DC or AC. The pref. sulphuric acid concn. is min. 20 wt.%, esp. 27.5 wt.% but also higher, and with a temp. above 20 degrees C., esp. 60-65 degrees C. but also higher; the pref. current density to achieve anodic polarisation is 0.1-5.0 A/dm.2 Process removes oxides from the surface of Al prior to coating with adhesive. No chromate is used which normally has to be continuously regenerated and also causes effluent problems; the adhesion of the coating to the Al is improved.