This technology demands that a workpiece is first removed from oil and rust, and then auxiliarily electroplated. Because the atom of metallic surface of electroplated workpiece is activated, molten Al and mother material can be better bound. The auxiliary electroplating agent has following components (wt.%): NH4F (5-15), NaF (30-40) and KF (45-65). The workpiece has been baked at 180-250 deg.C before hot-dipping calorization. The hot-dipping calorization is that a workpiece is put in a molten Al at 700-800 deg.C for 3-5 minutes. A covering agent is added on the surface of molten Al. Its components (wt.%) include KCl (40-50), NaCl (35-45) and Na3AlF6 (5-25). The workpiece after hot dipping is immediately put in cold water tank. |