WHAT IS THERMAL ANALYSIS FOR AEROSPACE ALUMINUM CASTING

Foundries can take different samples of the aluminum melt before and during the casting process to measure melt properties: RPT, chemistry, temperature, hydrogen, inclusions, oxydes and thermal analysis. The thermal analysis sample provides information on the solidification properties of the melt within 7 minutes on the shop floor. This is different from chemical properties. Recent advances in thermocouple signal processing allow automatic cooling curve analysis to provide more than the well-known grain refinement and eutectic modification potentials. Using a variant of the Newtonian approach, phases forming during solidification of the sample are measured as an energy % over the total energy absorbed or released. For aerospace casting applications, for example, this means that the presence of the Mg₂Si phase can be optimized in order to adapt the melt treatment for a specific foundry, as well as heat treatment cycles. The goal is to reach higher, more consistent mechanical properties with solid aluminum A356 according to AMS-A-21180 and avoid porosities. Measuring the solidification properties of aluminum A201.0 to exceed AMS-A-21180 Cl10 casting requirements allowed the melt treatment to be adapted for each batch depending on shop floor %humidity and use a higher remelt/new-ingot recycling ratio. The fraction solid curve from the thermal analysis result was used for casting filling and solidification simulation inputs. Filling the molds with the same melt quality using counter-gravity and gravity systems helps understand non-conformities; if the melt properties are the same, what else might be the cause of casting defects ? The metallurgical engineer has an easier time when he can measure what he needs to control.