| 2139 alloy is a new aluminum alloy developed by addition a small amount of Ag element to the Al-Cu-Mg alloy with high Cu:Mg ratio. The high damage tolerant, high heat resistance and high ballistic properties of 2139 alloy make it possible to be applied in the next generation ultrasonic transport airplane and some armor tanks. The study of this thesis focused on the homogenization, solution and ageing treatments of 2139 alloy. The microstructure and properties including heat resistance and fatigue properties of the alloy, as well the effect of Mn on the alloy, were also analized.The microstructure of both as-cast alloys has been studied. It is found that the grain size of 2139 alloy is large, and there is heavy segregation along the grain boundaries. Surface scanning of the as-cast 2139 alloy shows that Cu element is rich along the grain boundary, while both elements Mg and Ag are evenly distributed across the matrix. An optimized homogenizing treatment is performed at 520℃for 24h according to the thermal analysis by Differential Scanning Calorimeter (DSC) method and the microstructure characterization of as-cast 2139 alloy. The optimized solution treatment for 2139 alloy is also fixed as 520-525℃for 1.5-2h. The fit aging temperature can be chosen from160℃to 180℃.There are three exothermal peaks in the DSC curves of as-quenched 2139 alloy, each of which is corresponding to the nucleation and growth of the GP zone,Ωphase andθ' phase, respectively. Furthermore, the mechanical properties and microstructures after artificial ageing treatment at both 160℃and 180℃were compared. The research results show that 2139 alloy experiences three stages during aging treatment, namely underage stage, peak-age stage and overage stage. It cost 10-12h for 2139 alloy to reach peak ageing status and the peak strength is about 473MPa. When the alloy was aged at 180℃, only 4-6h is needed to reach the peak-aged status and the peak strength is about 479MPa. The strength of 2139 alloy declines faster at 180℃than at 160℃when the ageing treatment is extended to over-aged stage.The grain size of 2139 alloy with trace Mn element is smaller than that of 2139 alloy due to the refining effects of Mn element to the alloy, although there still is obvious segregation along the grain boundary. The homogenization treatment, solution treatment and aging treatment optimized for 2139 alloy are also applicable to alloy 2139 with Mn element, based on the fact that Mn element has no substantial effect on phase transformation of the latter alloy, either as-cast or as-extruded. The UTS of peak-aged 2139 alloy with Mn element decreased to 453MPa, compared with 474MPa of 2139 alloy, while the elongation gained to more than 15%, from about 10% of 2139 alloy. Both strength and elongation of 2139 alloy decline rapidly after going into over-aged stage, but neither changes much for 2139 alloy with Mn, even if hold for a relative long time after peak-aged stage, indicating that Mn element is helpful to improve elongation but detrimental to strength.The addition of trace element Ag to an Al-Cu-Mg alloy with high Cu:Mg ratio results in the Mg-Ag clustering along{111}Alplane due to the extremely high binding energy between Mg and Ag atoms, promotes the nucleation and growth ofΩphase there and, as a result of that, suppresses the nucleation and growth ofθ' phase.The microstructure of 2139 alloy during age treatment is also studied in this thesis. And it is found that theθ'phase would precipitate prior toΩphase at the early stage when the ageing temperature is relatively lower, and with time going on theΩphase becomes the main strengthening phase gradually. While the 2139 alloy was aged at a higher temperature, the precipitation ofθ'phase is suppressed at early stage, andΩphase precipitates preferentially along{111} Al habit plane to become the main strengthening phase. The images from HREM show that bothΩphase andθ'phase are coherent with the matrix. During aging treatment process, theΩphase grows by a step-control mechanism. At the same time, the alloying elements are redistributed, causing both Mg and Ag atoms to segregate toΩ/αinterface. The Mg-Ag atom-pair wall, therefore, forms to prevent the free diffusion of Cu atoms, helping restrain the growth ofΩphase along thickness direction.The STEM images further confirm the Ag atoms, with high atomic number, distributed at boundaries betweenΩ/αinterface. TEM images of 2139 alloy with Mn show that theΩphase is the main strengthening phase, with a small amount ofθ'phase and a thick-bar-like phase, too. The thick-bar-like phase is identified, with the help of EDS and diffraction pattern, as Al11Cu5Mn3, which is detrimental to the mechanical properties of the alloy.Different pre-stretch deformation by 2.5% and 5% were performed on as-quenched 2139 alloy, and then were artificial aged at 180℃immediately. It is found that a 2.5% pre-deformation increased the ultimate tensile strength (UTS) at peak-aged status by 11MPa, and a 5% pre-deformation contributed to an increase of 34MPa. However, the pre-deformation reduced the elongation of the alloy, and the more the pre-deformation was, the more it reduced the elongation. Pre-deformation doesn't affect the time to reach peak-aging status.Both peak-aged 2139 and 2139 with Mn alloys were held for 100h at 150℃,175℃, 200℃and 225℃, respectively, before the tensile test at room temperature. Then 2139 alloy with Mn shows a less loss of the strength after the exposure at high temperature than 2139 alloy, indicating the former one is more heat-resistant. Especially, the tensile strength of peak-aged 2139M alloy after being held at 150℃for 100h is almost the same as before heat exposure. Substantial strength loss is observed only when the exposure temperature is over 200℃.The endurance limit of peak-aged 2139 alloy is about 141MPa, lower than that of 2139 alloy with Mn element, which is 275MPa, indicating the latter one presenting better fatigue resistance. It is believed that the ternary AlCuMn phase in alloy 2139M can change the existence form of Fe impurity, which is helpful to improve fatigue resistance.
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