Shengping Wen

Geometric and Chemical Composition Effects on Healing Kinetics of Voids in Mg-bearing Al Alloys

The healing kinetics of nanometer-scale voids in Al-Mg-Er and Al-Mg-Zn-Er alloy systems were investigated with a combination of in situ transmission electron microscopy and electron tomography at different temperatures. Mg was observed completely healing the voids, which were then rejuvenated to the alloy composition with further aging, in the Al-Mg-Er alloy. On the contrary, Mg51Zn20 intermetallic compound was formed in voids in the Al-Mg-Zn-Er alloy, which leads to complete filling of the voids but not rejuvenation for the material. For voids with different geometrical aspects, different evolution processes were observed, which are related to the competition between bulk and surface diffusion of the alloys. For voids with a large size difference in their two ends, a viscous flow of surface atoms can be directly observed with in situ electron microscopy, when the size of one end becomes less than tens of nanometers.

Microstructural evolution of new type Al–Zn–Mg–Cu alloy with Er and Zr additions during homogenization

Abstract A comprehensive study on the microstructural evolution of a new type Al–Zn–Mg–Cu–Er–Zr alloy during homogenization was conducted by optical microscope, scanning electron microscope, transmission electron microscopy and X-ray diffraction analysis. The results show that serious segregation exists in as-cast alloy, and the primary phases are T (AlZnMgCu), S (Al 2 CuMg) and Al 8 Cu 4 Er, which preferentially locate in the grain boundary regions. The soluble T (AlZnMgCu) and S (Al 2 CuMg) phases dissolve into the matrix gradually during single-stage homogenized at 465 °C with prolonging holding time, but the residual Al 8 Cu 4 Er phase cannot dissolve completely. Compared with the single-stage homogenization, both a finer particle size and a higher volume fraction of L1 2 -structured Al 3 (Er, Zr) dispersoids can be obtained in the two-stage homogenization process. A suitable homogenization scheme for the present alloy is (400 °C, 10 h)+(465 °C, 24 h), which is consistent with the results of homogenization kinetic analysis.

The Microstructure Evolution of Al–Mg–Si–Mn–Er–Zr Alloy During Homogenization

The formation of non-equilibrium intermetallic phases during solidification significantly deteriorates the mechanical properties of Al–Mg–Si–Mn–Zr–Er alloy, but homogenization heat treatment can effectively reduce these residual phases. Therefore, it is necessary to study the evolution of these non-equilibrium intermetallic phases during different homogenization treatment. In this study, the methods we used are OM, SEM in combination with EDS, XRD and TEM. The results showed that non-equilibrium intermetallic phases between grains are mainly Al0.5Fe3Si0.5, Al0.7Fe3Si0.3 and Al5Mn12Si7. After homogenization, the main residual phase is Al5Mn12Si7. Compared with single homogenization, two-stage homogenization can effectively reduce the homogenization time and is good for the precipitation of fined Al3(Er, Zr) particles.

Effect of Erbium–Zirconium Composite Modifications on the Microstructure and Mechanical Properties of A356 Aluminum Alloy

The Al–7Si–0.3 Mg (A356) alloys with various contents of the rare earth element Er, Zr were prepared by the conventional casting technique. The effect of Er, Zr composite modifications on the microstructure and mechanical properties of A356 alloys was investigated using the optical microscopy (OM), scanning electronic microscopy (SEM), energy spectrum analysis and mechanical testing. The results show that addition of 0.3 wt% Er and Zr had an excellent refining effect on α-Al grains and a modification effect on Si containing phase in the as-cast state. The size of α-Al dendrite reduced, the acicular eutectic Si became short rod-shaped or granular. When Er and Zr content was 0.3 wt%, the tensile strength and hardness of the alloys reached up to maximum values.

Microstructure and Mechanical Properties of Hot-Rolled 5E83 Alloy

Hot-rolling plates of Al–4.5Mg–0.7Mn–0.2Zr–0.2Er alloy were prepared under the reduction of 50%, and tensile property, impact toughness were measured at the temperatures varying from 200–470 °C. The microstructure of the hot-rolling plates was investigated using scanning electron microscopy and transmission electron microscopy. The results showed that the tensile strength and yield strength decreased with the rise of the hot-rolling temperature, the elongation and impact toughness showed the opposite trend, and the best match between strength and toughness was at the rolling temperature of 350 °C. The second phase particles in the alloy had a great influence on the impact toughness and plasticity of the alloy. As the rolling temperature increased, the dynamic recovery and dynamic recrystallization occurred in the alloy. Dispersed Al3(Er, Zr) particles formed in the alloy when Er and Zr were added. The Al3(Er, Zr) particles were able to pin dislocation motion, hinder the growth of subgrains and the migration of grain boundaries, thereby inhibited the dynamic recrystallization of Al–4.5Mg–0.7Mn–0.2Zr–0.2Er alloy and its thermal stability improved.

Effect of RRA Treatment on the Properties and Microstructural Evolution of Al–Zn–Mg–Cu–Er–Zr Alloy

Effect of RRA treatment on the mechanical properties and microstructure of Al–Zn–Mg–Cu–Er–Zr aluminium alloy was researched by hardness measurement, conductivity measurement, exfoliation corrosion measurement, transmission electron microscopy (TEM). Discussed the relationship between the regression treatment and composite properties of the alloy. The study found that the hardness of RRA treated alloys first rise and then decline with the increasing of regression time, but the corrosion performance is increasing all the time. After pre-aging treatment 120 °C/24 h, regression treatment 180 °C/60 min, re-aging treatment 120 °C/24 h, the combination property of the alloy is optimal, the hardness, conductivity and the exfoliation corrosion grade are respectively: 207.6 HV, 33.53%IACS, PC. At this moment, it is found from the TEM observations that the matrix precipitates are small and dispersed, resemble to T6 temper. The grain boundary precipitation out phases are discontinuous distribution and the relatively wider PFZ, similar to the T73 temper.

Study of Aging Precipitation of Al-Zn-Mg Alloys with Er Additions by Monte Carlo Simulation

Our former experimental study showed that the addition of Er to Al-Zn-Mg alloys speeded up the aging precipitation, accelerated the precipitation of and enhanced the effect of aging strengthening distinctively. In this paper, the Monte Carlo method was applied to simulate the microstructural evolution of Al-2.6Zn-(2.3Mg)-(0.07Er), Al-2.6Zn-2.3Mg-(0.12Er), and Al-2.6Zn-2.3Mg-0.1(Er,Zr) alloys during aging. The effects of Er addition to Al-Zn-Mg alloys on the clustering of Zn and Mg atoms are studied through analysis of the simulation results and the effects on the subsequent aging process are discussed as well. The results show that the Zn/Mg/Er clusters appear beside the Zn clusters, Mg clusters and Zn/Mg clusters in the Er addition Al-Zn-Mg alloys. The Zn clusters and Zn/Mg clusters are finer in the Al-2.6Zn-2.3Mg-xEr alloys than that in the Al-2.6Zn-2.3Mg alloys without Er addition. The size of the Zn clusters and Zn/Mg clusters in the Al-2.6Zn-2.3Mg-0.07Er is eight percent and nineteen percent smaller than that in the Al-2.6Zn-2.3Mg alloys without Er addition respectively. This precipitation refinement effect of Er addition to the Al-2.6Zn-2.3Mg alloys is enhanced with the increment of Er content. These above results are consistent with the experimental results that the precipitation in the Al-Zn-Mg alloys with Er is finer and denser than that in the Al-Zn-Mg alloys without Er. The Er addition changes the clusters distribution in the Al-Zn-Mg alloys by its interaction with the main solute atoms and the vacancy, and thus influences the precipitations during subsequent aging processing.