Papers by Author: Zi Qiao Zheng

Abstract: An Al-3.43Cu-1.28Li-0.49Mg-0.12Zr containing 0.62Zn and 0.29Mn was designed and the microstructures and mechanical properties of the alloy with various heat treatments were investigated. The precipitates of the alloy consist of T1 (Al2CuLi), θ′ (Al2Cu)
σ (Al5Cu6Mg2) and δ′ (Al3Li). As solution temperature is changed from 485°C to 530°C, the solution degree of alloying elements in alloy increased, the amount of T1 in the alloy aged at 160°C for 18 h increased and that of θ′ is decreased, resulting in an increase of strength. After solution treatment at 530°C, the alloy aged for 18 h at 145°C is mainly strengthened by G P zones, and a little amount of T1 precipitates. As aging temperature is increased to 160°C and 175°C, the strength increased, due to the sufficient precipitation of σ and T1. The smaller amount of T1 in the alloy aged at 190°C is consistent with its lower strength. Meanwhile, it is found that the σ precipitate does not coarsen as aging temperature increases in the range from 160°C to 190°C.

Abstract: A systematic homogenization treatment on Al-Li-Cu-Mg-Mn-Zr alloy, within the temperature range from 500
C to 540
C for 24h or 36h was conducted. Microstructure and alloying elements distribution before and after homogenization treatment were studied by optical microscope, SEM, EDS and XRD. The results showed that in the as-cast condition Cu segregated at grain boundary and formed θ(Al2Cu) phase. With the homogenization temperature increased and time prolonged, the amount of the remained particles at grain boundaries decreased, and the alloying elements distribution became more homogeneous. It has been found that the homogenization temperature has more obvious effects on the microstructure and mechanical properties than time. However, the alloy homogenized at temperatures above 540
C was overheated. Furnace cooling generates large amounts of precipitates in the matrix. The best homogenization parameter of the Al-Li-Cu-Mg-Mn-Zr alloy was determined as 530
C for 24 h followed by air cooling.

Abstract: The microstructures of Al-0.2Sc and Al-0.2Sc-0.12Zr alloys have been investigated.The results show that Al3Sc and Al3(Sc1-xZrx) dispersoids exist in as-rolled Al-0.2Sc and Al-0.2Sc-0.12Zr alloy respectively, and their orientation is (001)α║(001)dispersoid, [010]α║[010]dispersoid.The Al3Sc particles in as-rolled Al-0.2Sc were precipitated from hot rolling process, while the larger Al3(Sc1-xZrx) particles in as-rolled Al-0.2Sc-0.12Zr from the solidification, and the small particles also from hot rolling process. There is segregation of Sc and Zr in the Al3(Sc1-xZrx) dispersoid, and Sc is rich in the outside shell while Zr rich in the core of the particles. It is believed that the grain and subgrain boundaries can be pinned by the Al3Sc particles when annealed after cold-rolling, and this may lead to restricting the recrystallization of the Sc-containing alloys.And it’s not until the dissolution of Al3Sc that the recrystallization can happen in this kind of alloys.

Abstract: The present paper outlines the effect of small addition of Sc,Ag and Mg on the ageing characteristics and microstructural evolution in some microalloyed Al alloys,such as Al-Cu-Mg, Al-Ag and Al-Li alloys.Small quantities of these microalloying elements can modify the ageing characteristics of these alloys,and significant changes have been found in their microstructural evolution after small microalloying element additions. The observed effects are explained in terms of the atomic behaviour during the early ageing stage,and one of the key factors governing this effect is Sc/Vacancy mechanism.

Abstract: The effects of trace Ce, Ag on the microstructure and mechanical properties of Al-Cu-Li alloy after thermal exposure have been investigated. It’s found that the addition of Ce may lead to a slight increase in mechanical properties after thermal exposure at 107  . The stability of T1 phase is enhanced by independent Ag addition and the combined additions of Ag and Ce,which results in higher strength compared with Ag-free alloy at 150  thermal exposure. However, at 200  exposure, a great number of q¢ precipitates at the expense of T1 may be responsible for higher tensile strength in the Ag-free alloy than that of the independent addition of Ag and combined additions of Ag and Ce alloys.

Abstract: The hot deformation behaviors and microstructure in Al-Cu-Li alloy containing small amount of Ag and Mg were investigated by transmission electron microscopy and isothermal compression tests.When the strain rate is 0.1, 0.01 and 0.001s-1(the deformation temperature within the range of 360-520􀀀 ) and 1 s-1(deformation temperature 520 􀀀 )respectively, the flow stress decreases after a peak value, showing dynamic recrystallization,while the steady-state flow characteristics exist on the other deformation conditions. The flow stress of Al-Cu-Li-Mg-Ag alloy during hot deformation can be expressed by a Zener-Hollomon parameter in the hyperbolic-sine function with the hot deformation activation energyDH of 250.45kJ/mol. The dislocations may climb with support from many vacancies generated during hot deformation, thus forming lots of helical dislocations. The dynamic precipitation and successive dynamic particles coarsening during hot compression have been assumed to be responsible for further flow softening when deformed at low strain rates.