The suitability of die cast parts for welding is highly dependent on the melt and pressure die casting process. It requires casting materials and melt and pressure die casting methods (see Vacural process, Vacuum systems by VDS SA Vacuum Diecasting Service) which ensure low gas absorption and oxide impurity during pressure die casting.
The design engineer typically places weld seams in low-stress zones; however, for a die casting, these should also be close to the gate. Fig. 1 shows the eight target levels of pressure die casting, the final one being a casting suitable for welding and heat treatment. Fig. 1 also illustrates the required steps of the pressure die casting process regarding venting, melt transport and the application of separating agents (see also Die cast separating agent).
Die cast parts made from the alloy AlSi9MgMn (Silafont-36) are particularly well suited for welding, both the standard MIG and TIG methods (see Gas-shielded welding processes) and laser beam welding. The AlSi5 or AlSi10 welding filler is preferred for welded structures with type AlMgSi0.5 wrought alloys. The weld seams or heat-affected zones between components made from wrought aluminum alloys and die cast parts made from Silafont-36 withstand alternating loads perfectly if the cast edges exhibit a low pore volume and are completely free of the oxide film after a possible T7 heat treatment (see Material condition and Heat treatment of hardenable aluminum alloys).
Fig. 2 states the mechanical values in the heat-affected zone. Unlike elongation, the strength values in this zone are hardly influenced. AlMg5Si2Mn (Magsimal-59) has a higher shrinkage rate and force than AlSi die casting alloys. Special die separating agents developed for the processing of this alloy improve flowability, the ability to slide during ejection, and therefore the suitability of the pressure die castings for welding.
Construction welding with castings made from the alloy Magsimal-59 uses the TIG method with AlMg4.5MnZr filler or laser/electron beam welding methods. Other than elongation, the strength characteristics in the heat-affected zone are hardly influenced. When using the SG-AlSi5 filler, the elongation values will be reduced even further. The mechanical properties indicated in Table 1 below which are applicable to manual MIG welding with the AlMg4.5Mn filler illustrate how the strength characteristics in the heat-affected zone are hardly influenced compared to elongation.
Gas-shielded welding processes
Shielding gas for welding
Hüttenaluminium-Gusslegierungen, product catalog, Rheinfelden Alloys GmbH & Co. KG, 2011.