use of fluidized sand bed as an innovative technique for heat treating aluminum based castings /

Abstract

The current study was carried out to arrive at a better understanding of the influences of the fluidized sand bed heat treatment on the tensile properties and quality indices of A356.2 and B319.2 casting alloys. For the purposes of validating the use of fluidized sand bed furnaces in industrial applications for heat treatment of 356 and 319 castings, the tensile properties and the quality indices of these alloys were correlated with the most common metallurgical parameters, such as strontium modification, grain refining, solutionizing time, aging parameters and quenching media. Traditional heat treatment technology, employing circulating air convection furnaces, was used to establish a relevant comparison with fluidized sand beds for the heat treatment of the alloys investigated, employing T6 continuous aging cycles or multi-temperature aging cycles. Quality charts were used to predict and/or select the best heat treatment conditions and techniques to be applied in industry in order to obtain the optimum properties required for particular engineering applications.The results revealed that the strength values achieved in To-tempered 319 and 356 alloys are more responsive to fluidized bed (FB) heat treatment than to conventional convection furnace (CF) treatment for solution treatment times of up to 8 hours. Beyond this solution time, no noticeable difference in properties is observed with the two techniques. A significant increase in strength is observed in the FB heat-treated samples after short aging times of 0.5 and 1 hour, the trend continuing up to 5 hours. The 319 alloys show signs of overaging after 8 hours of aging using a conventional furnace, whereas with a fluidized bed, overaging occurs after 12 hours. Analysis of the tensile properties in terms of quality index charts showed that both modified and non-modified 319 and 356 alloys display the same, or better, quality, after only a 2-hr treatment in an FB compared to 10 hours when using a CF. The quality values of the 356 alloys are more responsive to the FB technique than 319 alloys through long aging times of up to 5 hours. The 319 alloys heat-treated in an FB, however, show better quality values after 0.5 hour of aging and for solution treatment times of up to 5 hours than those treated using a CF. With regard to the quality charts of 319 alloys, heat-treated samples show that increasing the aging time up to peakstrength, i.e. 8 and 12 hours in a CF and an FB, respectively, results in increasing in the alloy strength with a decrease in the quality values, for each of the solution heat treatment times used. The statistical analysis of the results reveals that modification and heating rate of the heat treatment technique have the greatest positive effects on the quality values of the 356 alloys. Analysis of the interaction plots and of the main effects plots confirmed that the quality values of 356 alloys, as compared to 319 alloys, are more responsive to the FB than to the CF heat treatment technique. The silicon particle characteristics of th...

Effect of Zr Addition and Aging Treatment on the Tensile Properties of Al-Si-Cu-Mg Cast Alloys

“…The β-Mg 2 Si and θ-Al 2 Cu phases can be easily dissolved when the optimum solution heat treatment temperature and time are employed. The solution treatment temperature is determined according to the alloy composition and solid solubility limit; however, it must be lower than the melting point of the phases that exist in the as-cast structure to avoid incipient melting of these phases [15,16].…”