Thermal stability in fabricating hollow aluminum alloy products using the capillary shaping technique

Capillary shaping (CS) is a directional solidification technique by which hollow aluminum products with inner ribs, a variable cross-section, and a bent geometry can be fabricated. Therefore, CS is an attractive option for the manufacture of aluminum automotive frames with the optimal design. However, several processing parameters affect the thickness accuracy of the products because the product geometry is not defined by molds but by the meniscus shape and heat balance at the solid–liquid interface. In this study, the thermal stability of the CS technique and the thickness accuracy of commercial grade pure aluminum and Al–Si binary eutectic alloy hollow products fabricated under non-uniform thermal conditions were investigated using temperature measurements, solidification structure analysis, and thermal analysis based on experimental, analytical and numerical approaches. High thickness accuracy was achieved when the pulling process was carried out under thermally stable conditions, under which the effects of the thermal non-uniformity were canceled out by those of a change in height of the solid–liquid interface. The thermal stability was maintained when the pulling rate was below a critical value. Finally, factors affecting the critical pulling rate are discussed and a heat transfer model for critical pulling rate analysis is proposed.

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