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The Powdering Mechanisem Research of Galvannealed Steel Sheet Coating in Forming

Author: LiuZuo
Tutor: HeMingZuo；JiangSheMing
School: Kunming University of Science and Technology
Course: Materials processing
Keywords: GA steel Chalking Peel off Extrude Bending
CLC: TG174.44
Type: Master's thesis
Year: 2010
Downloads: 95
Quote: 1
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Abstract


Alloying hot dip galvanized steel sheets (referred to as GA steel, Galvannealed Steel Sheet) for its excellent corrosion resistance, coating properties, weldability and high surface strength advantages have been increasingly used in the automobile, but the GA most defects by the steel plate is galvanized workers are trying to solve the problem of the large number of coating powder and shedding. GA plate stamping process, in addition to meet the appropriate mechanical properties and surface properties, the size of the amount of coating powder directly affect the performance of the galvannealed board punching, coating damage not only affect the stamping process, but also deterioration of its corrosion resistance, and is easy to cause surface defects, affecting the appearance after coating. Therefore, while satisfying the other properties of the obtained anti-chalking good performance of the plating layer is an alloyed hot-dip galvanized steel sheet production technology developed difficulty. By observed in the scanning electron microscope vacuum chamber, stretching and bending deformation in situ, the GA steel samples of different degree of alloying of laboratory prepared plating pulverization process of GA steel sheet during the forming process, and using OM and SEM , XRD and electrolytic stripping method of sample organization and structure analysis, the use of the double cupping test GA steel plating anti-chalking performance study, based on the degree of alloying GA steel forming process coating chalking mechanism. The results show that the crack number increases due to alloying the GA steel plate coating few cracks in the coating / steel substrate, extended along the coating / steel substrate interface, so it's easy to form a coating spalling; the normal alloying the GA steel plate and over the alloying the GA steel plating crack large increase with the bending of the number of increase in the degree of deformation of crack, the crack in the δ phase formation, cracks extended to a direction perpendicular to the coating / substrate interface Г / steel substrate interface; severe over the alloy plating layer of GA steel sheet by tensile stress as the large number of cracks generated by the bending deformation of specimen at the side, crack Г phase generated extended to Г1 phase gradually extended to the coating surface in the direction perpendicular to the plating / steel substrate. GA steel coating before undeformed pre-cracks, with the increase in the degree of deformation by the pre-crack of the tensile stress in the coating is expanded first, and expanded when the deformation reaches a certain level, the coating internally generated new cracks. Compressive stress coating along the pre-crack cross-section perpendicular to the cross-section of the coating relative slip in the formation of dislocation. With the bending deformation degree increase, due to the GA steel alloying compressive stress coating did not change significantly; the normal alloying the GA steel plate and over-alloying the GA steel plating at the pre-crack formation of dislocation relative slip, with the iron content of the coating elevated relative slip of the coating increases the degree of serious over-alloyed the GA steel plate coating at the crack relative displacement occurs mainly in Г1 / Г interface to the coating surface, with the increase in the degree of bending deformation of the sample, the coating from the pre-crack Г1 / Г interface extensions, and the form of composite crack propagation to the surface of the coating.

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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 > Metal complex layer of protection
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