J. Dong
,
G.M. Lu
,
J.Z. Cui
金属学报(英文版)
In this study, reheating of liquidus semi-continuous east billets of 7075 Al alloy wascarried out in a resistance furnace, and the temperature contrast of the outer andthe center of the reheated billets was investigated, then the reheating microstructureswere investigated. Results show that: the difference of temperature between the outerand center is small and the difference of their microstructures are also small. Dur-ing reheating at 576° C the spheroidization of grains is significant after 5rain and norosettes are visible after 20min by optical microscopy. Similar observations were madeon materials reheated at 596° C, but the ripening process is faster. The grains growup to 30-60pm, fine enough for thixoforming.
关键词:
reheating
,
null
,
null
,
null
刘慧敏
,
何建平
,
杨滨
,
张济山
金属学报
采用原位反应喷射沉积法制备TiCp/7075半固态铝合金坯料,在600℃保温10-60 min, 研究半固态二次加热过程中合金的晶粒长大规律, 并与喷射沉积7075铝合金进行对比分析. 结果表明, 添加原位TiC颗粒后, 合金的晶粒长大指数由2增加到3, 晶粒长大速率明显减慢. 其原因是添加TiC颗粒后合金晶粒长大激活能增加1倍左右, 使得合金的晶粒长大更加困难, 显示出原位TiC颗粒对喷射沉积7075铝合金的晶粒长大具有显著的抑制作用.
关键词:
TiCp/7075铝合金
,
reheating
,
spray formed TiCP/7075 Al alloy
H.B. Wu
,
H.T. Jiang
,
S.W. Yang
,
D. Tang
,
X.L. He
,
null
金属学报(英文版)
Cooled in water after isothermal relaxation of deformed austenite for different times, an Nb-bearing microalloyed steel always exhibits synthetic microstructures, in which bainitic ferrite dominates. Dislocation configurations and distributions of strain induced precipitates inside bainitic ferrite of samples relaxed for different times were distinct. When compared with the austenite model steel, which maintained fcc structure even at room temperature, the strain induced precipitates were not found in the sample without relaxation whereas these were distributed outside dislocations in sample relaxed for 1000s. Most of the strain induced precipitates distribute along dislocations and pin dislocations in sample relaxed for appropriate time. After bainitic transformation, the dislocations formed in deformed austenite remain to be pinned by the precipitates. When these samples were reheated to and held at 650 or 700¡æ, the non-equilibrious microstructures tended to evolve into equilibrious ones. The sample relaxed for 60s displayed the highest thermo-stability, whereas microstructure evolution was the quickest in the sample relaxed for 1000s even though it was the softest prior to reheating. Dislocations inside laths got rid of pinning of precipitates, and their polygonization became the precursor to the evolution of microstructures during reheated and held, followed by gradual disappearance of lath boundaries caused by dislocation climbing. Finally, recrystallization occurred and polygonal ferrite appeared. By hardness measurement, it was found that softening is not a single process occurring during reheated, in which hardness fluctuates with time. There were two peaks in the hardness-time curve of each sample having undergone relaxation, while single peak occured in the curve of the sample not being relaxed. These results indicated that the thermo-stability of microstructures was determined by their history of formation to a considerable degree.
关键词:
bainite
,
null
,
null
,
null
刘勇
,
温亚成
,
李卫平
,
余广夫
,
李俊洪
,
林霞
钢铁钒钛
建立了三段步进梁式加热炉板坯加热过程数学模型,用全隐式有限差分法对数学模型进行离散化,开发了板坯温度场计算模型.采用该模型重点研究了板坯宽度对板坯中心温度变化过程的影响规律.研究结果表明,对于厚度为200 mm的板坯,当板坯宽度大于600 mm时,板坯中心温度变化过程与板坯宽度无关.以此为根据,优化了板坯加热工艺,达到了提高生产效率并节能减排的目的.
关键词:
步进梁式加热炉
,
板坯
,
加热
,
温度场
,
优化
赵新宇
,
刘洋
,
甄新刚
,
王海宝
,
王文军
,
邹扬
钢铁
制作直径10mm试样模拟铸坯表面,使用Gleeble-2000D热模拟试验机研究表面控制冷却下强冷和返温阶段板坯表面热塑性及组织形貌的变化规律,为表面组织控制冷却在立弯式板坯连铸机上的应用提供理论依据.研究结果表明:强冷阶段,魏氏组织和膜状先共析铁素体的形成造成试样塑性恶化.返温阶段,返温处理有效地消除了这种恶化,将试样断面收缩率最小值提高至40％以上.因此表面控制冷却在立弯式连铸机上应用时,强冷阶段应在铸坯进入弯曲段之前完成,铸坯可以在返温阶段进入弯曲段.
关键词:
表面组织控制冷却
,
强冷
,
返温
,
高温热塑性
,
金相组织
张复懿
,
刘慧敏
,
刘丽
,
李志芳
复合材料学报
采用原位反应近液相线铸造方法制备4.4%TiC_P/7075铝复合材料,在基体合金的液-固两相区间(477～635℃)的600℃分别保温10、20、40、60 min,水淬固定其半固态组织,应用Image Pro Plus软件测量平均晶粒尺寸,研究原位TiC_P对二次加热组织的影响.结果表明,原位TiC_P不仅使合金铸态组织直接转变为等轴品组织,而且在二次加热过程中,对晶粒的长大行为具有明显的抑制作用.在相同的二次加热条件下,TiC_P/7075铝复合材料的平均晶粒尺寸比7075基体合金减小了30～40 μm,更适合于半固态触变成形.
关键词:
近液相线铸造
,
原位TiC颗粒
,
二次加热
,
7075铝合金
刘丽
,
刘慧敏
,
张复懿
,
郭远河
复合材料学报
采用原位反应近液相线铸造方法制备Al_2O_3P/Al-Cu复合材料,对其进行二次加热,研究晶粒的形貌演变和长大规律.用光学显微镜观察组织结构,应用Image Pro Plus软件测量并统计出平均晶粒尺寸及合金液相体积分数,并与理论计算数值进行比较.结果表明,在590℃保温10～60rmin后,不含Al_2O_3颗粒的Al-6.8%Cu基体合金平均晶粒尺寸为89～132μm,液相体积分数为14%～26.8%,而3.6 wt%Al_2O_(3P)/Al-6.8%Cu复合材料的平均晶粒尺寸为73～107μm,液相体积分数为11.6%～20.9%.说明Al_2O_3颗粒在合金的二次加热过程中对晶粒长大行为及液相体积分数的增长均有明显的抑制作用,从而为优化半同态组织提供了一种新思路.
关键词:
Al_2O_(3P)/Al-Cu复合材料
,
近液相线铸造
,
二次加热
,
组织结构
X.T.Liu
,
J.Z.Cui
金属学报(英文版)
Microstructure evolution of wrought aluminum alloy extruded rods and the mechanism of liquid phase formation during reheating were investigated. And the relation between the volume fraction of liquid phase and the recrystallization microstructure was proposed. The results show that increase in reheating temperature and time can augment the volume fraction of liquid phase and accelerate the grain spheroidization, as a result of which the requirement of semi-solid forming can be satisfied. Due to the higher aberration energy of grain boundary, the melting point is lowered as a result of the easy diffusion of atoms. At higher reheating temperature the grain boundary melts, the growth of the recrystallized grain is inhibited and the grain is refined. The composition of the low melt-point phase along the recrystallized grains was determined using EDS. It can be seen from the experimental results that when the extrusion rod of the wrought aluminum alloy is reheated at 610℃ for 20min, perfect fine equiaxial grains can be obtained, the average grain size is about 66.34μm and the volume fraction of solid phase is about 68%.
关键词:
wrought aluminum alloy
,
null
,
null
胡勇
,
倪旭武
,
胡强
兵器材料科学与工程
研究二次加热过程中Al-0.3Ce合金半固态组织的演化.结果表明:随保温温度的升高,初生固相颗粒逐渐球化,尺寸减小;随保温时间的延长,初生固相颗粒的圆整度提高,颗粒尺寸先减小后变大;当保温温度为655℃、保温时间为90 min,可获得最优的半固态组织.
关键词:
半固态
,
显微组织
,
二次加热
