Papers by Keyword: 7055 Al Alloy

Abstract: The evolution of microstructure, precipitate size, volume fraction and integrated intensity of Al-8.0Zn-2.05Mg-1.76Cu (7055) and 7055-1.0Li alloys during isothermal ageing has been studied by transmission electron microscopy (TEM) and synchrotron-radiation small angle X-ray scattering (SAXS). According to the TEM results, referring to the thermodynamic phase diagram, it was found that the addition of Li changed the types of the precipitates. T1 phase was observed in the 7055-1.0Li alloy besides the GP zones, η' and η with variant orientations with matrix, η1、η2 and η4. The super-lattice spots of L12 (Cu3Au) structure were probably due to the existence of Al3Li (δ') or Al3(Zr,Li). Furthermore, the precipitation sequence has been modified in Li-containing Al-Zn-Mg-Cu alloys. The precipitate volume fraction derived from the integrated intensity for 7055 alloy reached an plateau except ageing at 120°C and the maximum was about 0.052-0.054 in the temperature range 140-160°C.

Abstract: A study was conducted on 7055 Al alloys processed by Equal-channel Angular Pressing (ECAP). The quantitative information about precipitate size, distribution and volume fraction in ECAPed samples was investigated by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). It is found that with the number of ECAP increasing, the quantitative information about volume fraction (fv), precipitate size (R), specific inner surface of particle-matrix (Sp), and integrated intensity (Q0) all increased, indicating that ECAP enhanced the nucleation and growth of precipitates. The microhardness of samples after two passes of ECAP is higher than that of T6 treated samples even after 96 h at 120°C. The formation of fine grains, higher volume fraction of precipitates, together with strain hardening induced by severe deformation are the main factors leading to a high microhardness in ECAPed samples.

Abstract: The grain growth behavior and mechanical properties in the friction stir weld zone after post weld heat treatment (PWHT) have been investigated. As PWHT temperature increased, a normal grain growth of as-welded equaxied grains ceased and abnormally grown grains with elongated shape coarsened. Huge elongated grains changed into smaller equaxied grains at 500°C. In case of lower heat input condition, abnormal grain growth initiated faster due to smaller initial grain size. The weld zone with bigger initial grains had advantages to maintain the thermal stability at high temperature. The hardness near the weld zone was almost recovered to the 95% of the unaffected base metal at 500 °C and the weld zone under lower heat input condition resulted in the homogeneous recovery through the whole weld zone.