Effect of strontium in soldering resistance
Extrusive effect has been taken in the area of die soldering study because such phenomenon is responsible to die failures. Die failure causes huge amount of maintenance cost and machines shutting down. Knowing the mechanism of die soldering and soldering resistance saves not only money but also reduces machine downtime. Industry has found that strontium, instead of iron conventionally, has significant effect in enhancing soldering resistance of H13 steel. Previous studies on strontium effect proposed the ideas that strontium changed the surface tension and wet angle of melting aluminum and also formed a layer on the melting surface. Thus, the diffusion between aluminum and iron was restricted. In this study, the author aimed to discover the oxide layer of strontium and verify the proposals. Approximately 0.03%wt to 0.05%wt of strontium in aluminum alloy can effectively reduce die soldering. In this thesis, the chemical and metallurgical effects of strontium were analyzed. Mold filling experiments and solidification simulation were conducted. Temperature gradient during solidification was studied. Microstructure including distribution of strontium and strontium oxide layer were studied by SEM and BSE. It has been found that strontium is segregated in the eutectic region, forming intermetallic phase and oxide.
Han, Purdue University.
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