表面粗糙度對鍍鋅層耐蝕特性之影響

本研究目的在探討表面粗糙度對於電鍍鋅耐腐蝕特性之影響。使用的試片以35ACR鋼材作為基底材料，將材料研磨成三種不同的表面粗糙度，分別是Ra在3.2μm到1.6μm之間，Ra在1.6μm到0.8μm之間，和Ra小於0.8μm，然後再電鍍鋅，其厚度為5μm及10μm，總共有六種不同的試片。接著這六種試片試片再進行中性鹽水噴霧試驗，每24小時觀察一次，共5次合計120小時後，記錄各時間點的腐蝕範圍。同時，另外製作金相觀察用試片探討鍍鋅層結合面結果，顯示表面粗糙度會影響電鍍鋅層的厚度落差，隨著表面粗糙度加大其落差也會加大。本研究在觀察鹽水噴霧試驗結果，顯示表面粗糙度越低耐腐蝕能力越好，在測試時間24小時到72小時之間，試片耐腐蝕能力差異最為明顯。由實驗比較的結果得到，改善電鍍鋅產品耐腐蝕能力，在不增加電鍍鋅層厚度的情況下，降低電鍍鋅前產品的表面粗糙度，也能有同樣的效果，甚至更優於增加電鍍鋅層厚度的效果。

關鍵字

表面粗糙度；電鍍鋅；鹽水噴霧試驗；耐蝕特性

並列摘要

The objective of this study was to investigate the relationship between surface roughness and corrosive resistance of zinc plated steel. The test piece was a 35ACR steel, in which its surface was grounded to three different levels of roughness, where they were respectively with Ra value from 3.2 μm to 1.6 μm, Ra value from 1.6 μm to 0.8 μm and Ra value less than 0.8 μm, before they were electroplated with zinc to the thickness of 5 μm and 10 μm, yielding a total of six different test pieces. The test piece was then subjected to a neutral salt spray test to be observed once every 24 hours for a total of 120 hours. The extent of corrosion at each time point would be recorded. The galvanized bonding layer on the surface of test piece was revealed under metallographic observation to show the impact on the electroplating thickness of zinc layer by surface roughness, which increased as the roughness increased. The salt spray test showed that lower surface roughness would have better corrosion resistance, especially the effect was significant from 24 to 72 hours of the test. By comparison, to improve galvanized product’s resistance to corrosion without increasing the electroplating thickness, the reduction of surface roughness could achieve the same outcome, and even better than the effect of increased zinc plating thickness.