Deng Yunlai

Effects of cryogenic treatment on mechanical properties of extruded Mg-Gd-Y-Zr(Mn) alloys

The influence of cryogenic treatment on the mechanical properties of the extruded Mg-Gd-Y-Zr(Mn) alloys was investigated by the tensile tests, scanning electron microscopy(SEM), transmission electron microscopy(TEM), and energy dispersive X-ray spectroscopy (EDS). The results show that the mechanical properties of both alloys are improved greatly during the in situ tensile test by soaking the samples in liquid nitrogen for 10 min. The ultimate tensile strength, yield tensile strength and elongation of cryogenic treated magnesium alloy added with zirconium or manganese are largely elevated. And remarkable microstructure change is observed in both alloys by cryogenic treatment. There are a large number of twins, rod-like, tree-like and chrysanthemum-like precipitated phases in the microstructures and the fracture surfaces exhibit the characteristics of ductile rupture when they are observed at room temperature.

INFLUENCE OF AGING ON THE HARDENABILITY OF 7055 ALUMINUM ALLOY THICK PLATE

The influence of aging on the hardenability of 7055 aluminum alloy thick plate was investigated by means of end-quench test,optical microscopy(OM),scanning electron microscopy (SEM),transmission electron microscopy(TEM) and differential scanning calorimetry(DSC).The results show that the hardenability can be improved by long time natural aging before artificial aging. The hardened depth is about 78 mm after natural aging and only about 45 mm after artificial aging, but increased to be about 100 mm after natural and artificial aging.During slow quenching,the coarseηequilibrium phase forms,and the solute concentration and vacancy concentration are decreased, which lead to larger and fewerη′hardening precipitates,thus lower hardness after aging.The long time natural aging before artificial aging is favorable for formation of stable GP zones at slowly-cooled locations,and consequently more amount of dispersed and fineη′hardening precipitates,which give rise to higher hardness and simultaneously better hardenability.

EXPERIMENTAL STUDIES AND CONSTITUTIVE MODELING FOR CREEP AGING OF 2124 Al ALLOY

A series of creep ageing tests under different temperatures and stresses have been designed to characterize the creep aging behavior of 2124 Al alloy,and the microstructure and properties of the samples in the interrupted tests have been observed.On the basis of the experimental results, combining the creep mechanism and age strengthening theory,a unified constitutive model has been developed for creep age forming of 2124 Al alloy.The constitutive relations,aging strengthening effect and the microstructure are closely correlated in the model,which could be suitable for different ageing temperatures and stress levels.Finally,the model has been used to predict the creep strain curves of added creep aging tests with different temperature,the computed results tally well with the experimental data.

Morphology Development and Kinetics of Plate or Rod Shaped Precipitates in Aluminum Alloys

Abstract Microstructure quantitatively analysis is significant for building the relationship between microstructure and properties, especially the ageing precipitation kinetics in aluminum alloys. In the present paper, a core parameter (aspect ratio) was introduced to describe the morphology change of precipitation. Aspect ratios of T 1 -plate precipitates in Al-Cu-Li-Zr alloys, S-plate precipitates in Al-Cu-Mg alloys and β -rod precipitates in Al-Mg-Si alloys were quantitatively analyzed. Results indicate that aspect ratios of precipitates increase at the early stage of ageing, then reach the peak and finally decrease slowly. The soft-impingement theory and HHC theory were introduced to model the ageing kinetics. Thermodynamics and kinetics parameters of different precipitates were also calculated in the model. Simulated results of different precipitates agree well with the experimental results.