Mechanical properties of Mg-6Gd-1Y-0.5Zr alloy processed by low temperature thermo-mechanical treatment

An as-solution treated Mg-6Gd-1Y-0.4Zr alloy was processed by low temperature thermo-mechanical treatments （LT-TMT）, including cold tension with various strains followed by aging at 200 °C to peak hardness. The results show that the precipitation kinetics of the alloy experienced LT-TMT is greatly accelerated and the aging time to peak hardness is greatly decreased with increasing tensile strain. The tensile yield strength, ultimate tensile strength and elongation at room temperature of the alloy after cold tension with strain of 10% and peak aging at 200 °C are 251 MPa, 296 MPa and 8%, respectively, which are superior to the commercial heat-resistant WE54 alloy, although the latter has a higher rare earth element content.

Effect of low temperature thermo-mechanical treatment on microstructures and mechanical properties of TC4 alloy

The effects of low temperature thermo-mechanical treatment （LTTMT） on microstructures and mechanical properties of Ti-6Al-4V （TC4） alloy were studied by optical microscopy （OM）, tensile test, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results confirm that the strength of TC4 alloy can be improved obviously by LTTMT processing, which combines strain strengthening with aging strengthening. The effect of LTTMT on the alloy depends on the microstructure of the refined and dispersed a＋fl phase on the basis of high dislocation density by pre-deformation below recrystallization temperature. The tensile strength decreases with the increase of pre-deformation reduction. The optimal processing parameters of LTTMT for TC4 alloy are as follows： solution treatment at 900 ℃ for 15 min, pre-deformation in the range of 600-700 ℃ with a reduction of 35%, finally aging at 540 ℃ for 4 h followed by air-cooling.

Fretting Wear Behavior of Medium Carbon Steel Modified by Low Temperature Gas Multi-component Thermo-chemical Treatment

The introduction of surface engineering is expected to be an effective strategy against fretting damage. A large number of studies show that the low gas multi-component （such as carbon, nitrogen, sulphur and oxygen, etc） thermo-chemical treatment（LTGMTT） can overcome the brittleness of nitriding process, and upgrade the surface hardness and improve the wear resistance and fatigue properties of the work-pieces significantly. However, there are few reports on the anti-fretting properties of the LTGMTT modified layer up to now, which limits the applications of fretting. So this paper discusses the fretting wear behavior of modified layer on the surface of LZ50 （0.48%C） steel prepared by low temperature gas multi-component thermo-chemical treatment （LTGMTT） technology. The fretting wear tests of the modified layer flat specimens and its substrate （LZ50 steel） against 52100 steel balls with diameter of 40 mm are carried out under normal load of 150 N and displacement amplitudes varied from 2 μm to 40 μm. Characterization of the modified layer and dynamic analyses in combination with microscopic examinations were performed through the means of scanning electron microscope（SEM）, optical microscope（OM）, X-ray diffraction（XRD） and surface profilometer. The experimental results showed that the modified layer with a total thickness of 60 μm was consisted of three parts, i.e., loose layer, compound layer and diffusion layer. Compared with the substrate, the range of the mixed fretting regime（MFR） of the LTGMTT modified layer diminished, and the slip regime（SR） of the modified layer shifted to the direction of smaller displacement amplitude. The coefficient of friction（COF） of the modified layer was lower than that of the substrate in the initial stage. For the modified layer, the damage in partial slip regime（PSR） was very slight. The fretting wear mechanism of the modified layer both in MFR and SR was abrasive wear and delamination. The modified layer presented better wear resistance than the substrate in PSR and MFR; however, in SR, the wear resistance of the modified layer decreased with the increase of the displacement amplitudes. The experimental results can provide some experimental bases for promoting industrial application of LTGMTT modified layer in anti-fretting wear.

Effect of Low Temperature Treatment on Agrobacterium-mediated Transformation of Maize Seed Buds

[Objectives]This study was conducted to improve the genetic transformation rate of maize. [Methods]The seeds of maize ＂ Zheng 58＂ as the experimental material were germinated and treated under freezing temperature of-18 ℃ for 30 and 35 min. The EGFP gene was transformed into the growth points of these seed buds by Agrobacterium tumefaciens EHA105. The transformation effect was determined by fluorescence protein detection on transformed buds. [Results]After a certain period of treatment at-18 ℃ following germination and transformation of maize bud growth points with A. tumefaciens,although the survival rate of maize buds was reduced,the percentage of transformed cells significantly increased. [Conclusions]Low temperature treatment can improve the transformation efficiency of A. tumefaciens to the growth point of maize bud.

Effects of Low Temperature Treatment on Bolting of Radish(Raphanus sativus L.)

[Objectives]This study was conducted to screen out a vernalization method of radish that is more suitable for breeding and hybrid production.[Methods]Eight radish inbred lines with different bolting tolerance were used as the research objects for the experiment.The following three treatments were done:(1)treating at 4℃in the dark with heat preservation for 1,2,3,4,and 5 weeks,respectively~([1]),(2)treating at 4℃in the dark with heat preservation for 3 weeks after 24 h incubation in light at 20℃,and(3)treating under light at a low temperature of 6.5℃for three weeks after cultivating under light at 20℃to 4 true leaves.The effects of low temperature treatment on the bolting and flowering time of different varieties of radish treated at different developmental stages were analyzed.[Results]When comparing these three methods,the low-temperature treatment of wet seeds had a better effect on early bolting of radish and is simpler and more feasible.The effect of treating four-leaf seedlings at 6.5℃was the worst;most radish inbred lines could shorten bolting time when treated at 4℃for one week;and within a certain range,the longer the 4℃treatment time,the better the vernalization effect.Different radish inbred lines had different performances to low temperature treatment.[Conclusions]This study provides a scientific basis for the theoretical research on vernalization of radish.