Abstract
The Al-Cu alloys have been widely used in aerospace, automobile, and airplane applications. Generally Al–Ti and Al–Ti–B master alloys are added to the aluminium alloys for grain refinement. The cooling curve analysis (CCA) has been used extensively in metal casting industry to predict microstructure constituents, grain refinement and to calculate the latent heat of solidification. The aim of this study is to investigate the effect of cooling rate and grain refinement on the thermal and thermodynamic characteristics of Al-Cu alloys by cooling curve analysis. To do this, Al-Cu alloys containing 3.7, and 4.8 wt.% Cu were melted and solidified with 0.04, 0.19, 0.42, and 1.08 K/s cooling rates. The temperature of the samples was recorded using a K thermocouple and a data acquisition system connected to a PC. Some samples were Grain refined by Al-5Ti-1B to see the effect of grain refinement on the aforementioned properties. The results show that, in a well refined alloy, nucleation will occur in a shorter time, and a undercooling approximately decreases to zero. The other results show that, with considering the cooling rate being around 0.1 °C/s, the Newtonian method is efficient in calculating the latent heat of solidification.
Highlights
Depending on the casting conditions and alloy composition, microstructure and properties of the different aluminium alloys will be different [1]
The following results were obtained: 1- With Considering the changes in the primary undercooling ( TRU) as the main factor to determine the effectiveness of grain refinement process, it was found that by grain refinement, the value of undercooling decrease approximately to zero
2- The results of microstructure and thermal analysis showed that the main effect of grain refiner is on eutectic solidification range
Summary
Depending on the casting conditions and alloy composition, microstructure and properties of the different aluminium alloys will be different [1]. Some of them were standardized such as DTA and DSC These techniques are very accurate and well documented, they are inadequate for industries to investigating solidification of metals and alloys. The other way for investigating solidification of metals and alloys is the cooling curve analysis method. This technique is based on recording and analysis of the temperature versus time data collected during the solidification of the sample. In recent years computer-aided cooling curve analysis (CA-CCA) has been used to determine thermo-physical properties of alloys, latent heat and solid fraction. The cooling curve does not always indicate all the reactions occurring during solidification of a casting clearly, due to the small amounts of heat evolved by certain phase transformations, so more sensitive techniques should be developed. As the enthalpy decrease in metal is equal to the heat transferred to the mold the mathematical form of the Newtonian analysis is given by the following equations [8,9,10,11,12]
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