Entity

Time filter

Source Type

Le Locle, Switzerland

Puga H.,University of Minho | Costa S.,University of Minho | Barbosa J.,University of Minho | Ribeiro S.,FEUP | Prokic M.,MP Interconsulting
Journal of Materials Processing Technology | Year: 2011

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 s 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 α-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. © 2011 Elsevier B.V. All rights reserved. Source


Puga H.,University of Minho | Barbosa J.,University of Minho | Gabriel J.,University of Porto | Seabra E.,University of Minho | And 2 more authors.
Journal of Materials Processing Technology | Year: 2011

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. © 2011 Elsevier B.V. All rights reserved. Source


Puga H.,University of Minho | Barbosa J.,University of Minho | Costa S.,University of Minho | Ribeiro S.,FEUP | And 2 more authors.
Materials Science and Engineering A | Year: 2013

The influence of high intensity ultrasound (US) propagating through a steel mold on the microstructure and mechanical properties of die-cast AlSi9Cu3(Fe), was studied for different levels of electric power and at different distances to the waveguide/mold interface. The effect of those parameters on the morphology of α-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 α-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 proposed. © 2012 Elsevier B.V. Source


Barbosa J.,University of Minho | Puga H.,University of Minho | Oliveira J.,University of Minho | Ribeiro S.,FEUP | Prokic M.,MP Interconsulting
Materials Chemistry and Physics | Year: 2014

The effect of applying ultrasonic vibration to the melt during cooling on grain structure, type and morphology of intermetallic compounds in AlSi9Cu3 (Fe) alloy was studied, as well as their nucleation mechanism. Detailed intermetallics analysis was performed using a combination of SEM/EDS and XRD techniques in order to obtain the most possible reliable information. Results show that without ultrasonic treatment a-Al17(Fe3.2, Mn0.8)Si2, a-Al8Fe2Si, b-Al9Fe2Si2 and Al2Cu are the intermetallic phases present in the as-cast samples. The application of ultrasonic vibration to the melt during cooling proved to be very effective in converting the a-intermetallics with Chinese script morphology to polyhedral crystals, suppressing at the same time the formation of the b-phase. Moreover, the application of this treatment only changes the morphology of a-intermetallics since its stoichiometry remains the same (a- Al17 (Fe3.2, Mn0.8)Si2). It was also verified that the application of acoustic energy to the melt promotes the change of a-Al grains from dendritic to a more globular structure. The ultrasonic treatment is also effective in promoting the fracture of polyhedral crystals of intermetallic phases, reducing their dimensions and causing their homogenous dispersion in the matrix. © 2014 Published by Elsevier B.V. Source


Puga H.,University of Minho | Barbosa J.,University of Minho | Teixeira J.C.,University of Minho | Prokic M.,MP Interconsulting
Journal of Materials Engineering and Performance | Year: 2014

Ultrasonic degassing of liquid metals has been studied over the last years, but it has been limited to laboratorial scale experiments of low volumes of melt. In this work, the combined effect of acoustic cavitation with metal agitation induced by the mechanical vibration of the ultrasonic radiator itself was studied, using a specially designed low frequency mechanical vibrator coupled to the ultrasonic degassing unit. Liquid motion in water was characterized by high speed digital Photron - FastCam APX RS video camera and Laser Doppler Anemometry to select the most favorable US and mechanical vibrator frequencies to induce suitable water stirring. Selected parameters were used to degas 10 L of AlSi9Cu3(Fe) alloy. A suitable piezoelectric sensor was used to measure sound pressure at different distances from the sonotrode to identify the zone of higher acoustic activity. Results have shown that melt stirring significantly improves US degassing efficiency (since it is possible to achieve almost the aluminum alloy theoretical density after 3 min processing time) which contributed to increase the tensile properties of the alloy. © 2014 ASM International. Source

Discover hidden collaborations