The Effect of Zinc-aluminum Coating on Hardness of 42CrMo Bolts

Zinc-aluminum coating(Dacromet) on 42CrMo bolts used in cars is measured before and after handling the workpiece in the microhardness images and Vickers hardness values,the results of which show that zinc-coated aluminum in surface has good permeability,and parts of surface increase to a certain hardness that the closer to the surface,the greater the hardness,the farther from the surface,the smaller the hardness,and the surface farthest from the heart department of hardness has no significant changes.The change of hardness is caused by shot preening.