Influência da temperatura de vazamento na microestrutura e dureza da liga fundida de alumínio A380 com adição do refinador 5Ti1B

Abstract

The aluminum alloy A380 has been used on a large scale in the industry due to its physicochemical characteristics of interest when high resistance to high temperatures is required. The variation of the cooling rate and the addition of different alloying elements results in different microstructural arrangements, which defines the alloy mechanical properties. This work evaluated the microstructural variation of the A380 alloy with the addition of a 5Ti1B refiner with different cooling rates when cast at temperatures of 650°C and 680°C and then the influence of these different microstructures on the mechanical properties of the ingot. Two aluminum A380 ingots were casted in conical metal molds, one at 650°C and the other at 680°C. From each ingot, 3 samples were taken from different regions along its length, enabling analysis of the upper, middle, and lower regions of each ingot. Subsequently, the samples underwent metallographic preparation so that a metallographic analysis became possible. The results indicated the presence of porosity in both ingots and similar microstructural characteristics, indicating that the variation in casting temperatures did not show a significant influence on the microstructural formation between the ingots. The samples taken from the lower region of both ingots showed reduced porosity, which was a determining factor for submitting only this region to scanning electron microscopy (SEM) for analysis of the microconstituents of the pieces. It was possible to observe, in the sample casted at 680°C, a higher presence of Silicon with an appearance of Chinese writing. Finally, the Brinell hardness test was performed with 4 hardness measurements for each sample, lower, middle and upper, at both temperatures in which the alloy was casted, 650°C and 680°C. When comparing the casting temperatures of the alloys, the results showed high average hardness values in the cast alloy at 680°C. Comparing the different regions of each ingot, it was observed that the lower region had higher average hardness in both ingots. The average hardness found in this region of both ingots was higher than the reference hardness value of the aluminum A380 alloy. The results point to higher hardness values in the alloy cast at 680°C, a fact that may be related to the greater presence of siliconrich phase in its morphology, when compared to samples casted at 650°C. However, this hypothesis can only be confirmed by performing Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) in a greater number of regions of the analyzed samples.