A Study on Corrosion Resistance of 6066 Anodic Film with Taguchi Method

• Main Authors: Chung-Chuan Ni, 倪忠川
• Other Authors: Hsin-Chih Lin
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/88676391759633575003

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 101 === 6XXX series aluminum alloys have excellent formability. For examples, the commonly used 6061-T6 alloy has maximum elongation of 17 %, and 6066-T6 alloy has maximum elongation of 12 % at room temperature. Although 6XXX alloys have lower strength than 2XXX and 7XXX alloys in as-wrought state, the strength of 6066-T6 alloy can be inceresed to near 400MPa after T6 treatment. Compared to 6061-T6, 6066-T6 has 100 MPa more increment in strength due to higher fraction of alloy elements, while these two alloys cost about the same. Therefore, it would be a good selection for aluminum plants. For this reason, we chose 6066 aluminum, and coated a protective film with anodic treatment. At first, we purchased 4 in. billet in order to solve problems directly during experiment. Experiments were proceeded in sequence with hot rolling, process annealing, cold rolling, and T6 treatment. Then, we prepared specimens identically for the following anodic treatment. For anodic treatment, we selected four important process parameters that influence the product quality (corrosion resistance) very much as four control factors in Taguchi''s method. These four parameters are Al2O3‧14 ~ 18H2O(s) addition, H2SO4(aq) concentration, current density, and working time. Furthermore, by selecting three appropriate levels for each factor, we can construct the L9 (34) matrix experiment. Then we proceeded two parts experiment and analysis of surface properties of anodic films. Eventually, we obtained an optimum condition of 6066-T6 aluminum anodic film for corrosion resistance at 9 g/l Al2O3‧14 ~ 18H2O(s) addition, 17 wt% H2SO4(aq), 1.2 A/dm2 current density, and 10 min working time. Results from polarization curve and 1392-hour neutral salt spray test show that corrosion current density can reach 10-10 scale (3 ~ 4 order increased compared to raw material) and has just 2.7 % corrosion area. It can provide excellent corrosion resistance certainty and hardness of 554 Hv. On our results, the anodic films should have excellent corrosion resistance, but they were still corroded. Thus, if we would like to obtain better anodic film, we should also consider physical defects except for an optimum condition in practice. We should reduce the content of impurities in our specimens before anodic treatment, For example, lower content limit of impurities is required for better control of charge during anodic process. Hence we can obtain excellent anodic film with less cracks. Keywords：6066 aluminum, anodic treatment, corrosion resistance, Taguchi method