| 8407 die steel is widely used as Al alloy die material and two of the major reasons for die failure are melting loss and thermal fatigue. Therefore, the two key factors, soldering and thermal fatigue, decide the service life of the casting die. In the present work, experiment of surface pretreatment was carried out in order to resolve the problem of soldering and melting loss.At first, the experiment of hot dip aluminizing was carried out in order to form Fe-Al alloy layer that might reduce the possibility of thermal fatigue crack by increasing the heat conductivity of the surface layer. But the Fe-Al alloy layer may increase the soldering tendency. So, the experiment of high temperature oxidation was carried out in order to form a layer of Fe-Al-O mixed oxide on the surface. This layer may reduce the soldering tendency and increase the service life of casting die by protecting steel substrate because of its unwettability. Some important results of this work are as follows.(1) Fe-Al alloy layer has been formed through hot dip aluminizing, the thickness of the Fe-Al alloy layer and the Fe/Al ratio vary with the aluminizing time and aluminizing temperature.(2) At the allowed temperature of casting dies heat treatment(below 600℃), the thickness of the oxide layer's is very thin or there is no oxide layer on surface after oxidation under CO2-CO or air atmosphere.(3) At the allowed temperature of casting dies heat treatment(below 600℃), the Fe-Al-O mixed oxide has been formed on Fe-Al alloy surface under pure oxygen atmosphere. It can protect steel substrate preferably, so this technological parameter is the appropriate surface processing technics that can be used for Al alloy casting dies.
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