Effect of Dissolution of η′ Precipitates on Mechanical Properties of A7075-T6 Alloy

The effects of dissolution of the η′ phase by solution treatment on the mechanical properties of A7075-T6 alloy were investigated. Immediately after solution treatment of the T6 sheet at 450 oC or higher, elongation significantly increased and dissolution of the η′ phase occurred. η′ is the main hardening phase. After natural-aging, GPI, which is coherent with the aluminum matrix, was formed and strength increased. When bake hardening after natural-aging was performed, the yield strength slightly increased due to partial dissolution of the GPI and re-precipitation of the η′ phase. In contrast, after solution treatment at 400 oC, there was less elongation increase due to the precipitation of the coarse η phase at grain boundaries and low dissolution of the η′ phase. In addition, when bake hardening after natural-aging was performed, the yield strength decreased due to insufficient GPI, which is the nucleation site of the η′ phase. To promote reprecipitation of the η′ phase, the solution treatment temperature was set to a level that would increase solubility. As a result, the yield strength was significantly increased through re-precipitation of a large number of fine and uniform η′ phase. In addition, to increase the effect of dissolution, a pre-aging treatment was introduced and the bake hardenability can be improved after dissolution.

Effect of Solution Temperature on the Microstructure and Properties of TB10 Titanium Alloy Bars

This paper studies the effect of solution temperature on the microstructure and mechanical properties of TB10 titanium alloy bars. The results show that the microstructure is composed of β phase and primary α phase (αp) when solution treatment is below the phase transition temperature. With the increase of the solution temperature, the β phase grain size in the microstructure increases, the thickness of the grain boundary decreases, and the number and size of the αp phase decrease, so that the strength of the alloy decreases and the plasticity increases. When the solution treatment temperature is 800°C, the reticulated grain boundary αp phase causes the plasticity to drop rapidly. When the solution treatment temperature is above the phase transition point, as the solution temperature rises, the β phase re-nucleates and grows, the grain size increases, the number of αp phase decreases. The super-cooled β phase grains induce martensite phenomenon due to stress, which eventually causes the strength and plasticity to decrease.

Deformation Mechanism Investigation on Low Density 18Mn Steels under Different Solid Solution Treatments

To meet the demand of the 10% weight reduction goal for automotive steel, the microstructure and mechanical properties of Fe-18Mn-Al-C steel with different carbon and aluminum contents were investigated under different solid solution treatments, and the deformation mechanisms of the experimental steels were elucidated. Aided by thermodynamic calculation, transmission electron microscopy (TEM) and in situ scanning electron microscope (SEM) analysis, it was shown that for the 18Mn-1.5Al experimental steel with about 20 mJ/m2 stacking fault energy (SFE), the twinning-induced plasticity (TWIP) effect always dominated in this steel after different solid solution treatments under tensile deformation. With the 7 wt% aluminum addition, the SFE of austenite was affected by temperature and the range of SFE was between 60 and 65 mJ/m2. The existence of δ-ferrite obviously inhibited the TWIP effect. With the increase in the solution treatment temperature, δ-ferrite gradually transformed into the austenite, and the n-value remained low and stable in a large strain range, which were caused by the local hardening during the tensile deformation. Due to the difference in the deformability of the austenite and δ-ferrite structure as well as the inconsistent extension of the slip band, the micro-cracks were easily initiated in the 18Mn-7Al experimental steel; then, it exhibited lower plasticity.

Characterization of Tensile Properties and Fracture Toughness of Equal Channel Angular Pressed Al-Zn Alloy

Influence of Equal channel angular pressing on mechanical properties and Fracture toughness of Al-Zn alloy were studied in present investigation. Samples are successfully processed using the ECAP technique for up to a four passes by using route A. Al-Zn alloys were heated to a solid solution treatment temperature at 550oC for 2 hours prior to ECAP, this treatment introduces the precipitates which were capable of obstructing motions of dislocation and improves the refinement of the grain during ECAP process Finally, artificial ageing was performed at a temperature of 190°C for 0-20 hours with an interval of 2 hr and specimens are cooledat room temperature with natural air.Fracture toughness was found experimentally for ECAP processed samples using SE (B) specimens according to ASTM E399 standard.Study revealed the enhancement in mechanical properties such as yield strength, ultimate strength and microhardness after four passes by route A technique.The improvement in the fracture toughness properties of artificially aged ECAP samples can also be due to dislocation strengthening, grain boundary strengthening, and the creation of much finer UFG grains, according to the results. Despite the increased tensile strength after ECAP, the ductility behaviour has decreased due to the precipitation of GP zones and dispersion of η, ή, T and E within the Aluminium matrix Furthermore, scanning electron microscope (SEM) micrographs revealed that ductile fracture with large dimples occurred in the artificial aged samples after the ECAP procedure.

Correlation between Solution Treatment Temperature, MicroStructure, and Yield Strength of Forged Ti-17 Alloys

The Ti compressor disks of aviation jet engines are produced by forging. Their microstructure, which depends on the forging conditions, strongly affects their mechanical properties. In this study, changes in the microstructure of Ti-17 alloy as a result of different solution-treatment (ST) temperatures and the related tensile yield strengths were investigated to elucidate the correlation between the ST temperature, microstructure, and yield strength. Ti-17 alloys ingots were isothermally forged at 800 °C and solution-treated at 750, 800, and 850 °C. The microstructure and yield strength were investigated for samples subjected to different ST temperatures. The primary α phase formed during the ST, and the secondary α phase formed during the aging treatment at 620 °C. The yield strength increased with increasing volume fraction of the primary α phase and increased further upon formation of the secondary α phase during the tensile test at room temperature. The correlation of the primary and secondary α phases with yield strength was clarified for tensile properties at room temperature, 450, and 600 °C. An equation to predict the yield strength was constructed using the volume fraction of the primary and secondary α phases.

Effect of Solid Solution Treatment on Corrosion Resistance of Al-Cu-Mg-Ag Alloy

In this experiment, Al-Cu-Mg-Ag alloy was used as material and solution temperature was used as variable to investigate its effect on the corrosion properties of the alloy and Hardness test, metallographic observation, electrochemical test, intergranular corrosion and exfoliation corrosion test were carried out on three groups of samples. The results show that the intergranular corrosion resistance of the alloy decreases with the increase of solution treatment temperature, and the sample treated at 505 °C has the best performance. This is mainly because grain boundary structure plays a role in increasing PFZ and expanding corrosion channels. The exfoliation corrosion resistance of Al-Cu-Mg-Ag alloy increases first and then decreases, and the sample treated at 515 °C has the best performance. This is due to the dual effects of grain boundary structure and grain morphology. On the one hand, the solution treatment temperature increases, which widens the precipitation-free zone and reduces the electrochemical corrosion resistance of the alloy. On the other hand, the increase of recrystallized grains decreases the cohesion of corrosion products and enhances the electrochemical corrosion resistance of the alloy.

Investigation of the Effect of Heat Treatment on the Microstructures and Mechanical Properties of Al-13Si-5Cu-2Ni Alloy

An experimental investigation was carried out to study the effects of solid solution treatment and aging treatment on the microstructures and mechanical properties of an Al-13Si-5Cu-2Ni alloy. The results show that the size of eutectic silicon decreased with solid solution treatment temperature increasing until 510 °C. Subsequently, the eutectic silicon size continued to increase as the temperature increased to 520 °C. Initially, the acicular eutectic silicon of the as-cast alloy was 10.1 μm in size. After the solid solution treatment at 510 °C, the eutectic silicon size was reduced to 6.5 μm. The θ′ phase is the main strengthening phase in the alloy, therefore, the effect of aging treatment on θ′ phases was explored. As the aging time increased, the diameter, length, and fraction volume of the θ′ phases were found to increase. The main reason for the improved performance of this alloy following heat treatment is the passivation spheroidization of the silicon phase and Orowan strengthening due to the θ′ phases. The optimal tensile strength of an Al-13Si-5Cu-2Ni alloy was obtained after solid solution treatment at 510 °C for 8 h followed by an aging treatment at 165 °C for 8 h. Therefore, this work has great significance for promoting the application of Al alloys at high temperatures.