Novel Concept to Detect an Optimum Thixoforming Condition of Al-Al₃Ni Functionally Graded Material by Wavelet Analysis for Online Operation

A novel technique to characterize the transition phenomenon from solid to melt of Al-Al₃Ni functionally graded material (FGM) through a wavelet analysis for the development of a thixoforming system is investigated. Identification of an optimum semi-solid condition for thixoforming is necessary not only for the construction of a system but also the fabrication of a near-net-shape product with fine microstructure. An online wavelet analysis system using Haar's wavelet function, which is applied for its simplicity compared with Daubechies' wavelet function, is developed to find the optimum operating condition. A thixoforming system, which is constructed adapting a threshold value as an index, monitors successfully a discontinuity of deformation of Al-Al₃Ni FGM with the temperature rise. Thus, the timing of an operation is not at pre-fixed temperature but at the time when the index related to a wavelet function is satisfied. The concept is confirmed to be suitable from the micro-structural observation of the Al-Al₃Ni FGM product, because the product under the optimum condition is found to have refined Al₃Ni grains, which change from coarse grains and are expected to improve the mechanical properties.