SYNTHESIS AND CHARACTERIZATION AT ALLOY Al-20% WEIGHT Si PREPARED BY MECHANICAL ALLOY

Abstract

The synthesis of alloys whose components show low miscibility, such as Al-Si, achieves in the mechanical alloy a method of amplifying this condition and generating microstructural changes that modify the properties of the alloy. Aluminum alloys containing 20% wt Si have been synthesized by mechanical alloying varying the grinding time and characterized by different techniques, in order to investigate the effect of grinding time on the microstructure, density and electrical resistivity. XRD measurements confirm the biphasic condition of the Al-Si system, identifying the presence of the characteristic phases Al-α and Si-δ, and detecting changes in the lattice parameters as a result of the formation of Al/Si solid solutions; A solid solution of Si in Al-α with a solubility of up to 3.14% at dissolved Si and a crystallite size of 30 nm is formed after 70 hours of grinding. The SEM-EDS study indicates a heterogeneous distribution of particles of different sizes that tend to be homogeneous for grinding times greater than 30 hours. Calorimetric studies detect a single endothermic reaction corresponding to said temperature at the beginning of fusion, in accordance with the phase diagram, and showing an increase in the enthalpy of fusion above the value of the silicon enthalpy. The density variation is directly associated with the synthesis, compaction and sintering processes. During the synthesis of the alloy, the electrical resistivity modifies its behavior from a metallic conductor to one of composite materials for long grinding times. This study corroborates the increase in the solubility of Si in Al, and its effect on the properties studied. It also reflects a gradual relaxation towards equilibrium of all the processes involved as the alloy consolidates with increasing grinding time.