溶融Al-Si-Mg合金めつき鋼板のめっき組成と腐食挙動

摘要

溶融アルミニウムめっき鋼板（以下，A1めっき鋼板）は，溶融亜鉛めつき鋼板と比較して耐食性が優れ，表面外観の意匠性（銀白色）に富んでいることから，塗装無しで長期間使用可能な表面処理鋼板として，自動車排気系材料を始め，屋根壁等の建材，各種熱器具材，自動車燃料タンク材，更に最近ではホットスタンプ工法を用いた超高強度自動車部材等への適用が広まりつつある。Alの融点は約660℃とZnに比べて高いために，溶融めつき時にめっき層と鋼板の界面に生成する金属間化合物の層(通常，合金層と称される)が厚く成長して，加工時にここを起点としためつき剥離などが起きやすい。このためめつき浴にSiを8〜10mass%添加して合金層の成長を抑制したTypeIという製品があり，加工性と耐熱性に優れる。%This study was intended to investigate the effect of the amount of Mg and Si addition in the Al-Si coating in order to improve corrosion resistance of Aluminized steel sheets. A salt spray test using formed specimens proved that Al-8mass%Si-6mass%Mg-coated steel sheet having less cracks in the alloy layer after forming has the best corrosion resistance. This outdoor exposure test using unformed specimens for10 years proved that corrosion weight loss of AI-8mass%Si-6mass%Mg-coated steel sheet was reduced to approximately 30%less than that of Aluminized steel sheets and approximately 70%less than that of 55% aluminum-zinc alloy-coated steel sheets; thereby, it was possible to confirm that Al-8mass%Si-6mass%Mg-coated steel sheet has favorable corrosion resistance under along-term atmospheric environment. This is supported to be the protective effects caused by corrosion products mixed with Si and Mg, since the current value of the cathode po- were reduced by approximately 40%less than that of aluminized steel sheet.