Effect of the Solidification Conditions on the Microstructures of AlSi_7Mg Alloy during Semi-solid Remelting

The effect of the solidification conditions on the microstructures was studied during partial remelting of AlSi7Mg alloy with the help of an electrical pipe-type fumace. The results show that the eutectic is remelted above all and α phases are gradually evolved into spheroidal shape,if the AlSi7Mg alloys shrmd strongly by rotating electromagnetic field during the first solidification are heated again to 589 or 597℃ and have been held for a short time (for example, 5~10 min), and moreover, the higher the holding temperature,the faster the eutectic remelting process and α phase's evolution are. In contrast even though the AlSi7Mg alloy's samples non-stirred with fine dendritic microstructures are heated to the same temperatures as those stirred by rotating electromagnetic field and have been held for 60 min,it is not possible to change all the dendritic a phases to speroidal α phase.     

变形高温合金纯净熔炼设备及工艺研究进展

本文试图对国内外近年来变形高温合金纯净设备及其熔炼技术的发展情况进行综述。文章总结了变形高温合金中夹杂物的分类方法,调研了国内外变形高温合金熔炼设备生产厂家,分析了真空感应熔炼炉、电渣炉、真空自耗炉的设备特点与技术,归纳了国内外变形高温合金真空感应熔炼、真空感应熔炼+保护气氛电渣重熔、真空感应熔炼+真空自耗重熔、真空感应熔炼+保护气氛电渣重熔+真空自耗重熔四类工艺的研究进展。最后提出了提升我国变形高温合金冶金质量与性能的一些建议。     

Ti表面改性Al涂层及其抗氧化性能

为了提高钛材的抗高温氧化性能,利用电弧喷涂工艺方法在工业纯钛表面制备了纯Al涂层,对喷涂态纯Al涂层分别进行炉中加热及激光重熔改性处理,以得到具有一定抗高温氧化性能的Ti-Al金属间化合物涂层.对改性处理后的试件进行了800℃/60 h的氧化试验.结果表明,经750℃/5 h炉中加热改性处理后,钛基体表面可形成厚约300μm的TiAl_3金属间化合物层,而经激光重熔改性处理后,钛基体表面形成的TiAl_3金属间化合物层较薄.经高温氧化试验后,炉中加热改性Al涂层的微观组织形貌未发生明显变化,而激光重熔改性Al涂层的微观组织形貌变化较为明显.相比于激光重熔改性处理,经炉中加热改性处理后Al/Ti试件的抗高温氧化性能更佳.     

Ultrasonic cavitation erosion of as-sprayed and laser-remelted yttria stabilized zirconia coatings

Cavitation erosion resistance of 8 wt.% yttria stabilized zirconia has been investigated in specimens prepared by atmospheric plasma spraying and laser remelting post treatment. The results indicate that as-sprayed coatings involve defects such as primary cavities and initial micro cracks inside a particle and among the interfaces of particles. When the specimens are subjected to cavitation erosion, the micro cracks initiate and coalesce along with chip removals. Laser remelting produces a dense glazed layer with some cracks though the coatings. With the increasing of erosion time, large pieces are delaminated from coating-substrate interface leading to a significant mass loss. However, the resistance of laser remelted coatings to cavitation erosion is significantly improved when they are impregnated with epoxy by vacuum castable mounting. The relationship between cracks formed inside the laser remelted YSZ coatings and their damage mechanism under cavitation is discussed.     

激光重熔对Ni/WC涂层组织结构的改善机制研究

为了进一步探讨激光重熔等离子喷涂金属陶瓷涂层的组织与性能。本文通过等离子喷涂设备在45钢表面上制备了Ni/WC金属陶瓷涂层,再进行激光重熔处理,然后利用SEM、XRD、Photoshop软件及显微硬度测试仪等分析测试手段研究了该涂层在激光重熔前后的组织性能变化。结果表明:激光重熔前涂层为典型的层状结构,基体与涂层的结合面为机械结合,涂层内有大量未熔WC颗粒,且XRD检测其高温作用使得喷涂颗粒发生分解,分解出的C元素与其他元素发生反应生成新的化合物,丰富了涂层的硬质相;激光重熔后涂层中颗粒细化,分布均匀且能消除涂层中大部分孔隙和WC团聚。WC再次发生分解,生成新的硬质相,与周围的Ni形成“软基相+硬质点”的组合分布,基体与涂层的结合方式由机械结合转变为冶金结合。孔隙率由7.02%降到了3.08%,显微硬度也相应提高,且涂层显微硬度比基体高了255HV。     

稀土在铝及铝合金的变质效果的研究

用x射线衍射、光学显微镜、扫描电镜和能谱等分析Al-10Ce中间合金的相组成和微观形貌,研究Al-10Ce中间合金对α-铝的变质处理效果及对α铝的长效性变质和重熔稳定性变质,并与钠盐变质进行对比。结果表明：Al-10Ce中间合金用量对变质效果的影响很大,Al-10Ce中间合金用量为0．30％左右时达到最佳变质效果,用量少变质效果差,用量过多则形成过变质。用Al-10Ce中间合金对α铝进行变质,可取得极好的变质效果,变质持续时间比钠盐变质剂更长久且具有更好的重熔稳定性。     

Electroslag Remelting Withdrawing Technology for Offshore Jack-up Platform Rack Steel Manufacturing Process

Offshore jack-up platform rack steel must exhibit high strength and toughness as well as excellent welding properties.A high-quality large ingot is a prerequisite for obtaining a high-performance rough part.The electroslag remelting withdrawing(ESRW)technology using a T-shaped mold and bifilar mode was introduced to replace casting technology.Numerical simulation of the ESRW process was performed to determine the distribution of the temperature and velocity fields and to determine the optimum process for producing rack steels.Several A514 Qslab ingots with dimensions of 0.32m×1.40m×4.00 m were produced using ESRW technology in an industrial plant.The industrial test indicated that slab ingots produced by the ESRW method exhibited uniform chemical compositions and compact macrostructures.A 115.4mm thick plate was produced from the rough ingot after 11 rolling passes.Samples were obtained from different positions in the steel plate to test the mechanical performance and examine the microstructure,and the results revealed that the properties of the steel plate satisfied ASTM standards.The ESRW process improved the tensile strength and toughness of the slab ingot,enabling significant improvements in the anisotropy and low temperature toughness,which are critical for the development of rack steel for offshore platforms.     

TM210A钢低倍环状花样挽救办法探讨

通过对TM210A钢真空自耗锻棒低倍环状花样料进行高温均质化和循环加热淬火处理,并对其再进行轧制后,对其性能进行对比分析。结果表明对中间坯进行高温均质化处理再配合轧制变形,可以在保证不影响性能的前提下,使环状花样不合料得到有效挽救。     

抽锭电渣重熔718塑料模具钢板坯锭的新工艺

针对大型塑料模具毛坯电渣锭凝固过程中产生疏松和偏析等缺陷,从改变大型钢锭凝固条件角度出发,试图将大圆钢锭改为等截面面积的扁锭,同时采用双极串联供电控制渣池的温度场,以达到提高钢锭凝固质量的目的.本文介绍了采用双极串联、T型结晶器,抽锭电渣重熔工艺生产了0.32 m×2.0 m×4.0 m的718塑料模具钢板坯工业试验,重熔板坯锭的检验结果表明,板坯锭成分、低倍等凝固质量显著提高.     

焊趾TIG熔修跟随超声冲击处理对焊接接头残余应力及疲劳强度的影响

采用焊趾TIG熔修跟随超声冲击处理工艺对SMA490BW钢超微弧焊接头进行处理,对超声冲击前后焊趾熔修区残余应力以及接头4点弯曲疲劳性能进行研究。结果表明:超声冲击后,焊趾熔修区残余应力由拉应力转变为对疲劳强度有利的双向压应力,纵向与横向残余应力平均消除率分别达到116%和158%;超声冲击通过增大焊趾角与焊趾半径,使焊趾熔修区应力集中程度降低22%;超声冲击可使接头疲劳强度提高70%。