Investigation on the effect of Zn interlayer and process parameters optimisation in the production of Al-SS bimetallic castings

The effect of Zn interlayer on the stainless steel insert in the fabrication of Aluminium-Stainless Steel (Al-SS) Bimetallic casting (BmC) is reported. The design of Experiments was conducted with pouring temperature (680°C–730°C), insert preheat temperature (100°C–400°C) and insert thickness (1–3 mm) as influencing process parameters to produce Al-SS BmC. The maximum bond strength of 25.33 MPa was achieved when the experimental conditions were 705°C pouring temperature, 250°C insert temperature and 2 mm insert thickness. Using Response Surface Methodology (RSM), the interaction between the process parameters has been studied and a second-order polynomial equation was derived for maximising the bond strength. The predicted maximum bond strength using RSM for the above experimental conditions is 26.75 MPa. The output of RSM was given to the Genetic Algorithm (GA) to identify the maximum bond strength at forbidden parametric values. The maximum bond strength predicted using GA by interpolation is 26.87 MPa. However, the three process parametric conditions are 707°C, 277°C, and 1.86 mm respectively for achieving the maximum bond strength in the given Al-SS BmC’s. Experimental validation of the above conditions was conducted and the results obtained confirmed the predicted bond strength value using the GA technique. Spiral morphology due to the formation of Zn₁₀Fe₃ intermetallics was observed at the Zn-SS interface when the pouring temperature increased to 730°C and this might have led to the reduced bond strength of BmC than the bond strength achieved at 705°C and 707°C. The formation of the Al-rich and Fe-rich solid solutions as reaction layer between Al and SS without the micro gap around 705°C may contribute to the significant increase in bond strength of produced BmC with different insert temperatures and insert thickness.