Determination of temperature-dependent crystallographic parameters of Al–Si alloys using in situ neutron diffraction

Accurate evaluation of temperature-dependent lattice spacings of individual phases in complex engineering alloys enables analysis and design of enhanced components for high-temperature applications. However, typical characterization techniques are limited to measurements at temperatures at which the alloy is completely solid state. In this study, in situ neutron diffraction was performed to determine the crystallographic parameters of several phases in unmodified and Sr-modified Al–6 wt% Si and A319 alloys from the start of solidification to 423 K. Approximately linear correlations were found for the interplanar spacings and lattice parameters of Al, Si, Al₅Mg₈Cu₂Si₆ and Al₁₅(Fe,Mn)₃Si₂ phases with temperature for the entire measured range. The greater concentration of lattice-contracting elements dissolved in the A319 solid solutions resulted in smaller lattice spacings and larger coefficients of thermal expansion than the same phases in Al–6 wt% Si, yet eutectic modification with Sr did not produce noticeable changes in the crystallographic parameters. The Si phase was found to have the largest thermal expansion coefficient misfit with the Al matrix. These findings offer significant insight into the development and mitigation of thermal stresses in the processing and operation of engineering components.