No abstract

No abstract

The microstructural evolution of Cu-based alloys during aging was studied using a quantitative metallographic method. Samples were cut from ingots of Cu-0.8wt%Cr and Cu-0.8wt%Cr-RE alloys. These were solution treated at 1000 ºC for 1.5h and subsequently quenched in water, then separately aged at 480 ºC for different durations. The microstructures were observed by optical microscope, and the characteristic geometric parameters of precipitated Cr phase, including volume fraction V V , face density N A , mean diameter and roundness, were measured. These data provided more details about the process of aging. The results showed that precipitation of Cr phase occurred in the form of particles during aging. Rare earth elements promoted the precipitation of Cr phase and dispersed Cr particles. The phenomenon of overaging came earlier in Cu-Cr-RE than in Cu-Cr. In the present work, the optimal aging time at 480 ºC was 2 hrs for the Cu-0.8wt%Cr-RE alloy and 3 hours for the Cu-0.8wt%Cr alloy.

The effects of S addition on the corrosion behaviour of Sn-9Zn solders in 3.5 wt-% NaCl solution were investigated using dynamic potential polarisation, electrochemical impedance spectroscopy techniques and weight loss measurement. The results indicate that S addition could obviously improve the corrosion resistance of Sn-9Zn solder alloy as revealed by much lower corrosion current density, higher impedance and the reduced weight loss. It is believed that the homogeneous microstructures of Sn-9Zn, especially the black refined Zn-rich phases are favourable to improve its corrosion resistance. SEM observations found that S addition might promote the formation of denser and more uniform corrosion products on the solder surface. The main corrosion product was Zn5(OH)8Cl2·H2O determined by EDS and XRD analysis.

To analyse the effects of loading pass and heating temperature on the deformation behaviour and microstructure evolution of 7075 cast aluminium alloy, multi-pass high temperature loading experiments on Gleeble-3500 thermal simulation compressor were carried out. The results indicated that under each loading, all the true stress-strain curves are typical dynamic recrystallization curves. As strain increases, the stress increases sharply and then basically remains unchanged when it reaches a maximum value. As temperature rise, the peak value of flow stress slightly decreases when the temperature is less than 350°C, whereas it increases slightly when the temperature is larger than 350°C. The grain was elongated perpendicular to the axis. Only a small amount of fine recrystallized grains were found to nucleate and grow at grain boundaries at a lower temperature (250°C). As temperature increased, the recrystallized grain gradually increases, and its proportion gradually also increases until the recrystallization is basically completed. The achievements can provide a guideline to select processing parameters for the processes of metal forming of 7075 cast aluminium alloy, such as ingot blooming, spinning and extrusion.