Papers by Keyword: Age Hardening

Abstract: It has been reported that scandium addition improved various properties of aluminum alloys. However, present authors can not find any reports about the addition of Sc to 6000 series alloys. In this study, Sc was added to 6061 alloy and various effects of the Sc addition on aging behavior were examined, comparing with Al-Sc binary alloy. In the STQ state, resistivity at 77K, ρD77, of 0.2%Sc added alloy (6061+Sc) was about 2.0n-m higher than the alloy of no addition (6061). The ρD77 increased in initial stage of isothermal aging up to 473K, then decreased. Though ρD77 of binary Al-0.176%Sc alloy began to decrease from 1.8Ms at 448K and 18ks at 523K, excess decrease in ρD77 of 6061+Sc corresponding to precipitation of Sc compounds was not clear. Peak value of the HV0.1 was decreased and peak aging time delayed by the Sc addition in aging up to 498K. However, softening by overaging was retarded by the Sc addition. These effects of the Sc addition are considered to come from vacancy trap by solute Sc atoms or interface between particles of Sc compound and matrix acting as vacancy sinks.

Abstract: Precipitate microstructures in Mg-2.0Gd-1.2Y-0.75Zn-0.2Zr alloy were investigated and the characteristic and mechanism of microstructure evolution in the alloy were discussed. Specific long-period 14H ordered stacking structure was formed at grain boundary of Mg matrix crystals by solution heat treatment at 773K and metastable β’ phase was formed during subsequent aging treatment at 498K in the Zn-added Mg-Gd-Y alloys. These structure and phase exist simultaneously at the peak-aged condition in the microstructure. Precipitate free zone (PFZ) of β’ phase does not exist at an interface between a 14H structure and Mg matrix inside the grain, however, PFZ exist near the edge of 14H structure at grain boundary. These results strongly suggest that high diffusion rate of solute atoms at grain boundary promotes the nucleation and growth of 14H structure.

Abstract: Phase separation behaviors of a quenched Cu-3.0at%Ti alloy, as well as crystallographic structures of Cu-20.7at%Ti alloy have been studied using transmission electron microscopy. The furnacecooled Cu-20.7at%Ti alloy are composed of a-Cu4Ti (Ni4Mo-type) and b-Cu4Ti (Au4Zr-type) with the orientation relationship of (011)a//(110)b, [100]a//[001]b. As-quenched Cu-3.0at%Ti alloy showed a modulated structure with the modulation length of about 4 nm. When aged at 723K for 8 hr, the a-Cu4Ti phase emerges within the modulated or tweed-like microstructure. Prolonged aging results in the growth of the a-Cu4Ti particles and the loss of coherency. It is likely that asquenched Cu-3.0at%Ti alloy decomposes spinodally at 723K, followed by polymorphous ordering; though the present study did not exclude, as an alternative path, a decomposition mechanism based on the catastrophic nucleation.

Abstract: Modern automobiles are built with a steadily increasing variety of materials and semifinished products. The traditional composition of steel sheet and cast iron is being replaced with other materials such as aluminum and magnesium. But low formability of these materials has prevented the application of the automotive components. The formability can be enhanced by conducting the warm hydroforming using induction heating device which can raise the temperature of the specimen very quickly. The specimen applied to the test is AA6061 extruded tubes which belong to the age-hardenable aluminum alloys. But in the case of AA6061 age hardening occurs at room temperature or at elevated temperatures before and after the forming process. In this study the effects of the heating condition such as heating time, preset temperature, holding time during die closing and forming time on the hydroformability are analyzed to evaluate the phenomena such as dynamic strain hardening and ageing hardening at high temperatures after the hydroforming process.

Abstract: Tungsten, molybdenum and cobalt were co-diffused into the surface of undecarburized 45 steel at 1150 °C for 6 hours by a double glow plasma surface alloying technique. A Fe-W-Mo-Co type gradient surface alloyed layer with very low carbon content was formed. Thickness of the surface alloyed layer is 225.2μm. Concentrations of alloying elements Co, W and Mo in the alloyed layer are mostly ranged from 21 to 14 wt.%, 12 to 6 wt.% and 7 to 5 wt.%, respectively. The concentrations of alloying elements basically meet the requirements of W11Mo7Co23 type age-hardened high speed steel. The alloyed samples were solution heat treated, ageing and high-temperature tempering. The results show that the surface alloyed layer formed on 45 steel exhibits very strong age-hardening property and anti-temper softening ability as the metallurgical age-hardened high speed steel, the surface age-hardened high speed steel on ingot and decarburized carbon steel.