Thermal-Expansion Coefficients and Grüneisen Parameters of bcc Li–Mg Alloys

The thermal expansion of eight Li–Mg alloys spanning the bcc solid-solution range (100–31-at.% Li) has been measured from 80° to 370°K using a fused silica dilatometer. The room-temperature linear thermal-expansion coefficients were determined for each alloy from cubic fits of the data between 250° and 370°K. It was found that the linear expansion coefficients of the alloys decreased from a value of 4.6±0.1×10−5 °K−1 for pure Li to 3.9±0.1×10−5 °K−1 for an alloy containing 31-at.% Li. The linear expansion coefficients for Mg-rich alloys are unusually high; the expansion coefficient decreases by only 15% over the solid-solution range, whereas the melting point increases by 190%. The unusual behavior of the thermal-expansion coefficients is in direct contrast with the compressibilities of the alloys which decrease rapidly with increasing Mg content. As a result, the room-temperature Grüneisen parameter increases from a value of about 0.95 for pure Li to 1.75 for the 31-at.% Li alloy.