Temperature Dependence of the Specific Heat and the Changes in the Thermodynamic Functions of a Bismuth-Bearing AZh4.5 Alloy

摘要

Technical aluminum with increased contents of iron, silicon, and other impurities is known not to be used in industry because of its low service characteristics. Therefore, the development of new compositions of aluminum-based alloys is a very challenging problem. According to the aluminum-iron phase diagram, promising compositions are the eutectic (alpha-Al + Al3Fe) and the hypereutectic composition, which have the minimum solidification range and correspond to iron contents of 2-5%. An AZh4.5 alloy with the composition Al + 4.5% Fe has been used as a model alloy subjected to modification with bismuth. The specific heat of the bismuth-alloyed AZh4.5 alloy has been measured. The temperature dependences of the changes in the thermodynamic functions of the alloys have been calculated. The temperature dependence of the specific heat of the bismuth-alloyed AZh4.5 alloy has been studied on cooling using a computer and the Sigma Plot program. The polynomials of the temperature dependences of the specific heat and the changes in the thermodynamic functions (enthalpy, entropy, and Gibbs energy) of the bismuth-containing AZh4.5 alloy and the standard metal (Cu) have been found; they describe these changes with a coefficient of correlation R = 0.999. It is noted that the specific heat of the initial alloy decreases as the bismuth content increases, and the specific heat increases with temperature. As temperature increases, the enthalpy and the entropy of the bismuth-containing and the bismuth-free AZh4.5 alloys increase and the Gibbs energy decreases.