Once welding occurs on the mold surface, a complex Fe-Al intermetallic compound phase will be generated and cause defects on the surface of the casting during the next die-casting cycle. The hard intermetallic phase also accumulates on the mold surface. Therefore, production must be interrupted and the welding products must be removed by polishing. This will lead to prolonged production time, wasted labor, and reduced mold life.

   Generally, according to different welding forms, "welding" can be divided into two types.

   The first type of welding is called "impact welding", that is, welding occurs at the entrance of the mold surface toward the cavity or the runner. These areas are generally violently impacted by the molten metal flow during filling, the surface temperature is high, the pressure is large, and the protective layer is easily damaged. Under the continuous washing of the die-casting alloy, the protective layer of the mold fails and the metal substrate is exposed. The alloy reacts with the matrix material to form a complex intermetallic compound phase. The intermetallic compound is hard and difficult to deform. Its cracking and peeling in the die casting will not only cause quality defects of the casting, but also take away the base material and expose the fresh surface. This cycle starts and ends, and the welding phenomenon gradually deepens. In severe cases, the mold surface will be affected. Corrosion and melting of mold materials. Therefore, it is necessary to remove and repair the damaged surface in time in the early stage of welding.

   The second type of welding is called "deposition welding", that is, the welding position is facing away from the gate or away from the runner. These areas are usually where surface treatments or mold lubricants cannot reach. Therefore, their surface conditions, temperature distribution, and pressure conditions are different from other places.

   Generally, the die-casting alloy has a lower temperature after reaching these areas, and its fluidity becomes worse. It is easy to solidify first. The contact time between the hot semi-solid alloy and the mold surface becomes longer. In addition, the surface state of the mold itself is not ideal, so It is easy to form FeAl intermetallic compounds. In multiple die-casting cycles, intermetallic compounds will gradually deposit in these areas with poor fluidity, and finally a serious welding will be formed, which will affect the die-casting production.

   Although different forms of welding occur in different areas of the aluminum alloy die casting mold, the welding that occurs has some common characteristics-that is, the welding surface of the mold surface generally shows a silvery white gloss.

The composition of the welded layer is often a complex Fe-Al intermetallic compound, and because the intermetallic compounds that make up the layer are thin, there are certain difficulties in analysis.

   But foreign researchers ZWChen and DTFraser etc. used X-ray diffraction to analyze the structure of intermetallic compounds generated by dipping H13 steel in molten Al-11Si-3Cu die-cast aluminum alloy. They believe that the welded layer consists of composite The intermetallic compound αbcc- (FeSiAlCrMnCu), the hexagonal αH- (Fe2SiAl8) intermetallic compound in the outer compact layer, and the η-Fe2Al5 intermetallic compound in the inner compact compact layer. The structure of the Fe-Al interface they photographed is very similar to the morphology of the Fe-Al interface obtained by the author's "immersion in H13 steel in ADC12 die-cast aluminum alloy" test.

   The amount of intermetallic compounds is very small, the welding surface layer is extremely thin, and the analysis method is limited. At the current stage, researchers at home and abroad can only perform a rough qualitative analysis on it. For the formation and development of welded layers, the quantitative analysis of intermetallic compounds will be the focus of future research.