Influence of ultrasonic melt treatment on microstructure and mechanical properties of AlSi9Cu3 alloy

A novel MMM (Multi-frequency, Multimode, Modulated) ultrasonic (US) technology was used to refine the as cast microstructure and improve the mechanical properties of a AlSi9Cu3 alloy. Ultrasonic vibration was isothermally applied to the melt for 120 seconds at different temperatures slightly above the liquidus temperature of the alloy, using different electric power values, before pouring into a metallic mould. The microstructure of the cast samples was characterized by optical and scanning electron microscopy and energy dispersive spectrometry. Ultrasonic vibration promoted the formation of small -Al globular grains, changed the size and morphology of intermetallic compounds and distributed them uniformly throughout the castings. Ultimate Tensile Strength and Strain were increased to 332 MPa and 2.9% respectively, which are 50% and 480% higher than the values obtained for castings produced without vibration. The microstructure morphology and the alloy mechanical properties were found to depend on the electric power and the melt temperature, and by using a suitable combination of these parameters it is possible to achieve high refinement efficiency by treating the melts in the liquid state

Influence of indirect ultrasonic vibration on the microstructure and mechanical behavior of Al-Si-Cu alloy

The influence of high intensity ultrasound (US) propagating through a steel mold on the microstructure and mechanical properties of die-cast AlSi9Cu3, for different levels of electric power and at different distances to the waveguide/mold interface. The influence of those parameters on the morphology of -Al and eutectic Si and on the volume of porosity were investigated and characterized. The morphological characterization revealed that the high intensity vibration not only promoted the formation of small -Al globular grains but also modify the eutectic silicon, as well as decreased the volume of porosity. Besides microstructure modification, US treatment improved the alloy mechanical properties, namely UTS and strain, which maximum values were 339 MPa and 2.9% respectively by comparison to the values obtained for castings produced without US vibration. A mechanism of eutectic Si modification based on theoretical-experimental analysis is proposedFCT - Fundação para a Ciência e Tecnologi

The inluence of processing variables on the ultrasonic degassing of molten AlSi9Cu3 aluminium alloy

The effect of high intensity ultrasound on the degassing of AlSi9Cu3 alloy using the novelMMM(Multi-frequency Multimode Modulated) technology was studied. Different ultrasonic parameters (power and frequency), melt temperature and processing times were tested and their influence on the degassing efficiency evaluated. RPT (Reduced Pressure Test) was used to evaluate the hydrogen content in the alloys and the samples porosity level and density. For the experimental conditions used in this research, it was found that ultrasonic frequency has no influence on the hydrogen removal rate that, in turn, strongly depends on the ultrasonic power, the processing time and the melt temperature. The experimental results suggest that the MMM ultrasonic technology is an important improvement to the fixed-frequency ultrasonic systems by significantly decreasing the processing time to achieve a quasi-equilibrium hydrogen concentration in aluminium meltsFCT - Fundação para a Ciência e Tecnologi

Evaluation of ultrasonic aluminium degassing by piezoelectric sensor

The purpose of this work was the development of a reliable technique to evaluate the intensity of acoustic cavitation during degassing of aluminium melts and to use it to select the optimum processing time for an envisaged degassing efficiency. A high sensitivity piezoelectric disk type device was used as a sensing feedback in water and liquid AlSi9Cu3 alloy. The signal acquisition and processing was carried out on a dedicated LabVIEW® based application which allowed real-time monitoring of the piezoelectric sensor’s data and ultrasonic parameters. Standard Fast Fourier Transform was applied to obtain the dominant frequencies, as well as the sub and ultra-harmonics. It was found that the amplitude of the FFT sub-harmonic (f/2) was the best indicator to evaluate the process degassing efficiency, and it could be used to select the optimal processing time, independently of other variables. The developed methodology was applied to several AlSi9Cu3 melts, and validated by measuring the final alloy densities and the volume fraction of porosities, revealing that it is an efficient, fast and cost effective technique to evaluate the degassing treatment of aluminium alloys. Experimental curves of AlSi9Cu3 alloy degassing efficiency as a function of f/2 amplitude are presented for different degassing times.FCT - Fundação para a Ciência e Tecnologi

The combined effect of melt stirring and ultrasonic agitation on the degassing efficiency of AlSi9Cu3 alloy

The combined effect of high intensity ultrasound and melt stirring on the degassing of AlSi9Cu3 using simultaneously the novel MMM (Multi-frequency Multimode Modulated) ultrasonic technology to promote cavitation, and low frequency mechanical vibration to induce melt stirring, was studied. On a first stage single low frequency mechanical vibration experiments were carried out in water in order to visualize and characterize its individual effect on the liquid dynamics. On a second stage ultrasonic vibration combined with different mechanical vibration frequencies, melt temperatures and processing times were tested in liquid AlSi9Cu3 alloy and their influence on the degassing efficiency was evaluated and compared with the results of the single MMM ultrasonic degassing technique. Fixed ultrasonic parameters (frequency and electric power) were used, according to the best results obtained in former experimental works developed by the authors. For the experimental conditions used in this research, it was found that melt stirring significantly improves degassing efficiency, and such improvement depends on the metal temperature and the mechanical vibration frequency. The experimental results suggest that combining melt agitation and ultrasonic vibration it is possible to achieve almost the aluminum alloy theoretical density without increasing the processing time.FCT - Fundação para a Ciência e Tecnologi