铝合金板温成形和热成形技术应用研究

为解决强度高的铝合金板材冷成形时塑性差、容易开裂及回弹量大等问题,铝合金温成形和热成形技术受到关注。对铝合金板温成形和热成形的特点进行了论述,对于5×××系铝合金,温、热成形可有效提高合金成形性能,实现对形状复杂零件的成形,但强度不会增加;而对于6×××系或7×××系铝合金,采用固溶处理-成形-冷模淬火(HFQ)的热成形工艺可获得兼具复杂形状和高强度的零件。并从工程应用角度,介绍了目前国内外HFQ铝合金热成形技术在汽车应用方面的最新进展。最后以7075-T6铝合金为例,阐述了用该工艺制备高强度铝合金零件的优势和未来国产化应用需要解决的难点。

Macrosegregation and thermosolutal convection-related freckle formation in directionally solidified Sn−Ni peritectic alloy in crucibles with different diameters

Different from other alloys,the observation in this work on the dendritic mushy zone shows that the freckles are formed in two different regions before and after peritectic reaction in directional solidification of Sn−Ni peritectic alloys.In addition,the experimental results demonstrate that the dendritic morphology is influenced by the temperature gradient zone melting and Gibbs−Thomson effects.A new Rayleigh number(Ra_(P))is proposed in consideration of both effects and peritectic reaction.The prediction of Ra_(P) confirms the freckle formation in two regions during peritectic solidification.Besides,heavier thermosolutal convection in samples with larger diameter is also demonstrated.

A Simple Bio-preservation Technique to Increase Shelf Life of Ampalavi Mango Fruits Using Aloe vera Gel

Aloe vera is being identified as a potential medicinal plant for its application in industries as well as traditional usage. The gel obtained from the leaves of A. vera has numerous properties. In this study, using the gel to extend the shelf life of Ampalavi mango fruits was studied. Even sized, uniform coloured, matured Ampalavi cultivar mango fruits were surface cleaned and coated with 33%, 66% and 100% gel, respectively. Results revealed that the ripening was delayed due to the coating. The total soluble solid （TSS）, pH and weight loss were high in uncoated fruits. The mean pH of the pulp from fruits kept as control was 4.94 at 4 d fruit preservation period （FPP） and was slightly increased to 5.43 within 12 d FPP, whereas the minimal pH （4.69 at 4 d FPP and 5.03 at 9 d FPP） was noticed in 100% gel coated fruits. The TSS （brix） was significantly in higher levels （13.67°Bx within 4 d FPP and 20.77°Bx within 12 d FPP） in control fruits, whereas the minimum TSS value was 9.27°Bx and 18.03° Bx within 4 d and 12 d FPP, respectively, recorded from the 100% gel coated fruits in storage. The weight loss percentage （WLP） was significantly （P 〈 0.05） higher in control fruits （8.46%）, whereas the lower WLP （1.13%） was found in 100% gel coated fruits after 12 d of storage. This low-scale gel coating technique prolonged the fruits shelf life by delaying the fruit ripening. This effect has to be further investigated to commercialize the natural product for large scale ready-made application.

Effect of Different Shading Practices Used at Pre-harvest Stage on Quality and Storage Life of Sultana Seedless Grapes

Covering the grapevine rows to delay maturity and thus the harvest date becomes a widespread practice at Sultana seedless vineyards. The research work was carried out with different covers to examine their effects on grape quality and storage life in 2009 and 2010. Grapevines were covered with three different densities （shading ratios： 35%, 55%, 75%） at the veraison period. Unshaded （0%） control grapevines and grapevines shaded under different ratios were covered with polypropylene cross-stitch just before harvest maturity. Grapes under cover were harvested nearly one month after than those maturing under open conditions. Grape clusters were packed in PE bags and pre-cooled after harvest and then SO2-generating pads has been put on top, bags were sealed. In the second year at the 120th day of the storage, decay development has been observed in all applications. Total soluble solids content, maturity index and a＊ colour value were found lower in 55% and 75% shaded grapes compared to unshaded grapevines. Still, berry removal force and hue angle value in 55% and 75% of shaded grapes were higher than unshaded grapes. Effects of shading ratios on these parameters decrease or disappear at the end of storage.

Microstructural evolution during solution treatment of thixoformed AM60B Mg alloy

The microstructural evolution and kinetic characteristics were studied during solution treatment of AM60B Mg alloy prepared by thixoforming. The results indicate that the microstructural evolution includes two stages： the first stage involves rapid dissolution of eutectic β （Mg 17 Al 12 ） phase, homogenization and coarsening, and the second stage is regarded as normal grain growth consisting of primary α-Mg particles （primary particles） and secondary α-Mg grains （secondary grains）. In the first stage, the dissolution completes in a quite short time because the fine β phase can quickly dissolve into the small-sized secondary grains. The homogenization of Al element needs relatively long time. Simultaneously, the microstructure morphology and average grain size obviously change. The first stage sustains approximately 1 h when it is solutionized at 395 ℃ Comparatively, the second stage needs very long time and the microstructure evolves quite slowly as a result of low Al content gradient and thus low diffusivity of Al element after the homogenization of the first stage. The growth model of primary particles obeys power function while that of the secondary grains follows the traditional growth equation in the first stage. In the second stage, both of the primary particles and secondary grains behave a same model controlled by diffusion along grain boundaries and through crystal lattice.

Studies on the Compositional Properties of Main Miben Series Pumpkin Varieties in Southern China

Pumpkin is among the most popular agricultural products in Southern China. To determine the important analytical properties(dry matter, total soluble sugar,dissolvable polysaccharides, mineral content, electricity conductivity, soluble solid content, fruit weight, fat, protein, fiber, pectin, β-carotene and edible rate) of pumpkin in Southern China, this study investigated the physical and chemical properties and texture of raw and steamed pumpkins of 13 Miben series varieties. Miben pumpkins were frozen at-40 ℃ for 24 h, or at-4 ℃ for 24 h, or were steamed for 15 min in boiling water to investigate the effect of different treatments on the textural change, and to reveal the texture and sensory properties of the different varieties. A total of 13 pumpkin varieties of Miben series CP1578, CP2116, XM2-2,Baimi II, Guangmi I, Guangzhouluxia, Jintong, Laojinhanzaoshu, Quanguanjixiang,Newzuhe III, V pumpkin, Zaoshutianmi and Daguomiben were involved in this study.The results showed that the Miben series pumpkins had significant difference in physical properties. The editable rate of Miben series pumpkins was higher than77%. Chemical properties varied among different varieties. Textures of pumpkin flesh after different processes were different. In the sensory assessment of Miben pumpkins, the varieties with overall quality scores more than 50 were Guangmi I, Laojinhanzaoshu, V pumpkin and Daguomiben, indicating that the four varieties all had excellent properties.

变形-热处理流程对6082铝合金组织的影响

为了探明不同变形和热处理流程对6082铝合金微观组织和力学性能的影响规律,开展了6082铝合金的常规成形、退火-成形以及固溶-成形3种实验,并对微观组织和力学性能进行了表征。结果表明,退火和固溶处理可以减少挤压态试样中小角度晶界的比例,并有效地弱化其单一的强S织构。在400℃/0.1 s^(-1)变形时,退火-成形和固溶-成形工艺可以有效避免常规成形出现异常晶粒长大的现象;在500℃/0.1 s^(-1)变形时,退火-成形和固溶-成形工艺下试样的平均晶粒尺寸比常规成形试样的平均晶粒尺寸有所增加。工艺实验结果表明,采用固溶-成形工艺,6082铝合金锻件的抗拉强度可达到276.0 MPa,略低于常规成形锻件的283.6 MPa,但可以显著减少锻件粗晶,为高质量6082铝合金锻件的生产提供了一种新的路线。