The formability and corrosion resistance of color coated sheet are the main items to be selected. In the aspect of processing formability, the main requirements are as follows:
(1) Yield characteristics. If the color coated sheet is placed for a long time and the effect of aging is considered, it must be leveled before forming. When the temperature is increased by coating baking, the aging phenomenon will be aggravated. If steel
with very low carbon content should be used when non aging is strictly required.
(2) Shape preserving properties. Generally speaking, when the yield stress is small and the work hardening index n is large, the elastic recovery phenomenon is reduced.
In the process of sheet forming, because of the non-uniform change of elastic-plastic stress in the forming surface, uneven elastic recovery will occur. Generally, the material with low yield ratio (65 / 6b) is beneficial to shape retention.
Formaility. The formability of color coated sheet stamping process is not only related to the shape of material and die, but also to the characteristics of material itself. The material with small yield stress and high elongation has good tensile formability.
In addition, high N value is conducive to uniform elongation and good drawing formability. The plastic strain ratio y is the most closely related to the deep drawing property. The higher the y value is, the better the deep drawing property is.
Rigidity. Here the rigidity refers to the rigidity of the formed plate when the pressure is applied in the vertical direction. The panel with small curvature and flat shape is prone to sag and bulge. Therefore, the curvature should be considered to determine
the reasonable thickness. The corrosion resistance of the substrate mainly includes the corrosion resistance of the bare plate, the corrosion resistance after forming and the sacrificial protection diagram of the cutting edge.
After comparing the
corrosion resistance characteristics of various kinds of coated steel sheets, it is considered that under the condition of no high temperature (350 ~ 50 ` C) oxidation resistance, hot dip galvanized aluminum steel sheet (Zn + 5% Al + re (mg) commercial
name Galfan) is recommended as the best. Its corrosion resistance is 2 ~ 4 times higher than that of hot-dip galvanized sheet. Its processability is equivalent to that of electroplated sheet, and its cost is almost equal to that of commonly used hot-dip