Experimental Study on the Anomalous Internal Friction above Room Temperature in Cold-Worked AlCu Dilute Solutions

Abstract

Variations of internal friction and elastic modulus versus strain-aging time, temperature, and strain amplitude of cold-worked 99.999% Al, Al−0.10, −0.29, and −0.50 wt% Cu specimens are measured at and above room temperature by the free decay method in an inverted torsion pendulum. Similar to the case of AlMg, four internal friction peaks versus temperature (P1′, P1′, P2, and P3) are observed. The accompanying variation of the modulus curve and the shift of the amplitude peak with a change of measurement temperature are also similar to the corresponding cases of AlMg. The only difference is concerning the relative position of P1′ and P1′ peaks in the two cases, which may be attributed to the different relative atomic radii of Cu and Mg in the Al matrix. The variation of the position of the strain-aging peaks with changing Cu content and the appearance of an accompanying amplitude peak as well as its shift with strain-aging time give strong support to the dragging—break-away model. The influence of initial excitation strain amplitude on the amplitude peak is discussed.