7A52铝合金原位加热过程中的物相转变与热膨胀系数测量

Investigation of phases and thermal expansivity of 7A52 alloy in in-situ heating

用原位加热X射线衍射方法测量了7A52合金铸锭在不同温度下的X射线衍射谱,确定不同温度下该合金中存在的物相,精确计算基体在不同温度下的点阵常数和不同温度区间的热膨胀系数。试验结果表明:7A52合金铸锭由基体、少量η(MgZn2)、T(Mg32(Al,Zn)49)相和难熔相Al6Mn组成;随温度升高,合金元素从基体中析出形成η和T相,在300℃左右T相大量析出;T相在高于300℃的温度下逐步回溶入基体,形成单一固溶体。在低于100℃和高于450℃的温度区间内点阵常数变化主要受温度影响,而在介于以上温度的中间区段点阵常数变化平缓,基体点阵常数的变化受温度和相变双重因素影响。采用高温原位X射线衍射方法测量物相的热膨胀系数是可行且精确的。

The high temperature phases, lattice constants and coefficient of thermal expansion of the 7A52 aluminum alloy at different temperature have been measured by in-situ high-temperature X-ray diffraction method. The results show that the 7A52 alloy ingot consists of matrix, a littleη （MgZn2）, T （Mg32 （Al,Zn）49） and Al6Mn. Zn and Mg atoms precipitated from Al matrix and transformed into η and T phase with increasing temperature,precipitation arrived at the maximum at near 300 ℃. T phase re-dissolved into Al matrix when the temperature was higher than 300 ℃ and then the alloy transformed into the single solid solution. Lattice constant of Al matrix was function of temperature when the temperature was lower than 100 ℃ or higher than 450 ℃ ,but the lattice constant changed slowly when temperature was between 100 ℃ and 450 ℃. The change of lattice constants was influenced by both the temperature and phase transformation. As a new method of measuring thermal expansivity, the in-situ high temperature X-ray diffraction method is useful and accurate.