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Research on Welding and Corrosion Characteristic of Hot Dip Aluminized Coatings on22MnB5Steel Surface

Author: LiLei
Tutor: HanFei
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: 22MnB5steel sheet Hot-dipping Aluminum Gas tungsten arc welding Corrosion resistance
CLC: TG174.4
Type: Master's thesis
Year: 2012
Downloads: 30
Quote: 0
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Abstract


The surface treatment can improve corrosion resistance of steel, increase theirservice life, and will also reduce the amount of raw materials, which is applied inengineering widely; moreover a series of scientific issues are brought with thesurface treatment research, which has great scientific significance. The22MnB5steel is one of the ultra-high strength steel, which is suitable for hot stamping in theautomotive industry. In this study, the effect of dipping Al coatings of22MnB5surface on hot processing is clarified in two aspects: welding and corrosion resistant.The processes of hot-dipping-Al coatings on22MnB5surface are optimized. What’smore, the welding characteristics and corrosion resistance of the welding seam isalso investigated in this paper. It is studied that the effects of Al coatings on thewelding characteristics through metallographic test, SEM, EDS and tests of weldedjoint mechanical properties. And corrosion resistance of different Al coatings andwelding seam is characterized.The10%K2ZrF6and5%KCl is employed as a plating assistant agent.Obtained by measuring the coatings’ thickness and micro-hardness: the aluminumlayer thickness is about40μm under the conditions of720℃and80s, with fineappearance and low micro-hardness. Electrochemical corrosion tests and thefull-soak corrosion test demonstrate that corrosion resistance of the steel with hotdipping Al coatings is increased.The softening zone in the heat affected zone is the weakest part of the weldingjoint of aluminized22MnB5steel. When the heat input is low, the joint tensilestrength increased with the increase of the heat input. However, the joint tensilestrength decreased when the heat input increased to a certain extent.The weldingheat input is appropriate at about3800J/cm, and the highest welded joint strengthcan reach830MPa. The iron aluminum alloy layer does not affect the mechanicalproperties of welded joint, but makes the required heat input increase, such as theuncoated steel’s optimum heat input is3500J/cm around. As the existence of toothick aluminized coatings, the welding strength of aluminized steel, which areprepared in laboratory, can only reach500MPa. And the welding input need moreheat input. The heat input of different dipping process corresponding to the bestmechanical properties is4000J/cm.The corrosion resistance of the welding seam is analyzed through electrochemical measurements and the full-soak corrosion test. Compared with the basemetal and the aluminized coating metal, the corrosion resistance of the seam is decreased. But the corrosion resistance is better than the welding joint of base metal.The corrosion resistance of welding joint with different parameters is varied. Theresistance is decrease with the increase of heat input. After reaching the minimumcorrosion resistance, the corrosion resistance of welding seam is increase. Thewelding with heat input at3866J/cm has the minimum corrosion resistance.The variety regulations of the mechanical property and corrosion resistance of thewelding joints with different welding heat input are different. In practicalapplication, the suitable welding parameters can be chose by working conditionrequirements. Sometimes mechanical properties is important, and sometimesantic-corrosive performance is, or good comprehensive properties.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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