Study On The Die Soldering Of Hypereutectic Aluminum Alloys Used In High Pressure Die Casting

B390 alloy(ASTM sandard)is widely used in the automobile industry,such as in engine blocks,pistons,and brake cylinder bodies.It is widely known for its good wear resistance and high hardness.However,B390 alloy has a tendency to solder to the steel mold in which it is casted,especially in high pressure die casting.This phenomenon is known as die soldering.It is a major drawback to using B390 in the industry as it leads to production halts for cleaning the die,and eventually to the failure of the die.The die soldering mechanism has been studied in the past on hypo-eutectic alloys,but almost no attention has been given to hyper-eutectic alloys.The objective of this research is to analyze the mechanism on hyper-eutectic alloys and to establish a relevant method to prevent die soldering on B390.The B390 samples were cut from permanent mold-casted samples,produced by GM and imported from the United States of America.Our first aim was to characterize the factors influencing the die soldering mechanism,to confirm previous work which had been carried on die soldering.To do so,hot-dip aluminizing experiments were carried on H13 rods dipped in a B390 aluminum melt,melted in a SiC crucible in a microwave furnace.The rods were then extracted,cooled at room temperature,cut,polished to carry an EDS analysis on the section of the rod using a Scanning Electron Microscope.The results of the test confirmed previous works on the influence of temperature,time,and gate velocity on die soldering.However,some steps of the mechanism as it occurred in previous works occurred in a different order with B390.Our second aim was to analyze the causes of these discrepencies.After verification,it was also shown that the same mechanism occurred for A380.The high silicon concentration of B390 and to a lesser extent A380 considerably affected the first step of the mechanism.In addition,it was exposed that the mechanism was not only diffusion-driven,but that a chemical reaction step also participated to the mechanism.Finally,acknowledging the steps of the mechanism with B390,a method was used to attempt to prevent die soldering.A chromium coating was applied the alloy combined with a nitride surface layer.