Practical Method for Quality Testing of Phosphate Coatings on Cold Rolled Automobile Steel Sheets

The quality of phosphate coatings on cold rolled automobile steel sheets was judged by electrochemical technology. The relation currve between the open circuit potentials of phosphate coatings and time was tested in phosphate solution by constant current/potentiostat. The quality of phosphate coatings was determined at the inflection point time of the curve. The results indicates that when inflection point time(t)≤300 s, the quality of phosphate coatings is weak; when 300 s＜t≤700 s, the quality of phosphate coatings is common; when 700 s＜t≤1 000 s, the quality of phosphate coatings is good; when t＞1000 s, the quality of phosphate coatings is excellent.