Process And Properties Of Zn-Al Co-cementation On Medium Carbon Steel

To form the Zn-Al alloy layer on 42CrMo medium carbon steel by chemical heat treatment was the purpose of this paper.By comparing the structure and properties of the layers under different processes,the optimized process parameters for practical application were determined.Devices and equipments such as optical microscope?OM?,scanning electron microscope?SEM?,were used to observe the structure and morphology of layer.X-ray diffractometer?XRD?were used to analyzed the phase of layer.By salt spray test and electrochemical workstation,the corrosion resistance of the pure zinc layer and the Zn Al co-cementation layer were compared.Results showed that the thickness of the layer increases with the increase of temperature,and increases with increasing holding time.The appropriate process parameters of Zn-Al co-cementation finally is:heating temperature is 400?,holding time is 3h,the content of aluminum in agent is 10%¹6%,the mass ratio of Zn and Al is 3:1.It can be found that the material of Zn-Al co-cementation surface layer is composed of iron and zinc compounds,respectively zeta phase(FeZn₁₅)and delta phase(FeZn_10.98).The zeta phase has equiaxial crystal in the outside layer,delta phase is columnar crystals in the inner layer.Aluminum is dissolved in iron zinc compounds and no obvious Fe-Al intermetallic compounds were found.The time of the red rust come into being on pure zinc layer is 50 h,and which of Zn-Al co-cementation layer is 127 h.To compare with the sherardized layer,the corrosion resistance of Zn-Al co-cementation layer improved obviously.In the 3.5%NaCl solution,the corrosion current density of Zn-Al co-cementation layer was about 3.061×10^-8?A/cm²,which was smaller than that of sherardized layer.It can be concluded that the corrosion resistance of the layer is optimized because of the addition of aluminum.