Análise microestrutural e da microdureza de ligas Al-Si-Cu obtidas por solidificação unidirecional descendente

Abstract

The range of applications in which aluminum competes with other materials become necessary to the development of specific compositions and any other techniques in order to satisfy engineering requirements. These aluminum alloys show significant application potential as a material for sliding bearings due to their characteristics, mostly their low weight and possibility of compositions with elements of lubricating properties dispersed in their matrix. The Al-Si alloy combines high corrosion resistance, good weldability and low density, and has a wide range of physical and mechanical properties that depend of the microstructure and silicon content. With adding the Cu element, they tend to increase the mechanical strength of the alloy and fatigue strength, without loss the good castings characteristics. The present study has the objective to analyze the microstrutucral variations (dendritic spacings secondary, presence of second phases) of the alloys AL-5.5%Si-3%Cu, Al-7.5%Si-3%Cu and Al-9%Si-3%Cu and the correlaction with the Solidified unidirectionally descending under transient heat flux conditions in a vertical configuration device. The results show that with the addition of the solute there was a decrease in secondary dendritic spacings and consequently the increase in microhardness. And as the solidification front increased there was an increase in secondary spacing. It is also noted that as the positioning of the thermocouples moves away from the refrigerated base there is an increase in the solidification time. Can be observed also the rise of new phases like Al2Cu, Al+α. Thus the alloy Al-7,5%Si-3%Cu presents the best properties, when compared to the other alloys studied.