浇注温度对亚共晶Al-Si合金组织和硬度的影响

研究了不同浇注温度对亚共晶Al-Si合金的组织和硬度的影响。结果表明,在不同浇注温度下浇注时,得到的合金显微组织有较大差别。在660℃浇注得到的基本上是枝晶组织;而在615℃浇注,得到的则基本是球状和近球状的晶粒组织,可以成为优良的半固态触变成形坯料。另外,浇注温度对合金的硬度没有明显的影响。     

浇注温度对亚共晶Al-Si合金组织和硬度的影响

研究了不同浇注温度对亚共晶Al-Si合金的组织和硬度的影响.结果表明,在不同浇注温度下浇注时,得到的合金显微组织有较大差别.在660℃浇注得到的基本上是枝晶组织;而在615℃浇注,得到的则基本是球状和近球状的晶粒组织,可以成为优良的半固态触变成形坯料.另外,浇注温度对合金的硬度没有明显的影响.     

半固态过共晶Al-Si合金显微组织中近球形α相形成机理的研究

在电磁搅拌法制备的半固态过共晶Ａｌ－Ｓｉ合金的微观组织中发现了大量的近球形α相,实验证明,这种近球形α相是在共晶温度５７５℃以上开始同的。并且在重新加热至固液两相区５７５－５９０℃内保温一段时间后,这种近球形α相仍然存在,理论分析表明,在电磁 电磁搅拌产生的局部微区的高压作用下,过共晶Ａｌ－Ｓｉ合金熔体中Ａｌ原子偏聚团发生合并、长大而形成α相晶核,并且α晶核生长在电磁搅拌的作用下成为近球状。     

喷射沉积过共晶铝硅合金热处理工艺的研究

采用正交试验法对喷射沉积过共晶铝硅合金挤压坯的固溶+人工时效处理工艺进行优化,研究固溶和人工时效的温度及时间对挤压态合金组织结构的影响,测定不同热处理后合金的硬度和耐磨性,确定最佳的热处理工艺.结果表明,固溶温度、固溶时间、时效时间和时效温度对过共晶铝硅合金组织和性能的影响依次降低.并得 出最佳的热处理工艺为520℃×3h 固溶+120℃×10h时效,处理后合金的硬度为84.4HB,相对耐磨性为原始挤压态试样的1.22倍.     

磷元素对过共晶铝硅合金的影响

铝硅合金中的硅相由于晶粒粗大并且有尖锐的棱角,严重削弱了合金的机械性能,通常我们采用变质处理工艺来改善这一现象。通过实验我们证实磷元素能够显著改变组织的尺寸,通过对磷元素的扫描电镜和透射电镜分析,发现磷元素不仅作为形核核心,而且把硅相分割为很多小的晶块,使不同的小晶块生长方向各不相同,在宏观上观察,经过磷元素变质的硅相,形状上变得比较的圆滑。     

锶变质近共晶Al-Si合金力学性能与枝晶α数量之间的相关性

研究了锶的加入量对近共晶Al-Si合金中枝晶α形态的影响，采用定量金相分析软件测量了中枝晶α数量，并通过线性拟合分析了完全变质合金力学性能与枝晶α数量之间的相关性，研究结果表明，锶的存在促进柱状枝晶的生长并导致枝晶α数量的大幅度提高；力学性能指标与枝晶α数量间是高度线性相关的，枝晶α在提高合金力学性能中起着至关重要的作用。     

亚共晶Al-Si合金变质及凝固特性的研究

本文所研制的热分析装置用于快速测定铝硅合金的组织细化和变质效果,能在三分钟内完成测试过程.本热分析装置的特色是(1)采用了高精度,多功能的测试仪器,它不仅可以测出温度与时间的关系曲线,还能测试相应的微分曲线,其温度绝对误差△T≤±0.3℃;(2)对热分析样杯作了一系列试验.确定了适合铝硅合金的热分析样杯结构及材料,从而提高了测量结果的准确性和重复性.本文系统研究了Ti,Na,Sb,Sr,Re对亚共晶铝硅合金的变质及其对热分析曲线上特征值的影响,获得了能评估其变质程度的热分析判据.用Na,Sr,Re变质时,从未变质到变质良好,共晶生长温度TEG,共晶形核过冷度△TE;呈减小的趋势,共晶过冷度△T则呈增加趋势.用Sb变质时,从未变质到良好变质,△TE和△T呈增加趋势,7EG呈减小趋势,随着Ti量的增加,α初晶形核最低温度升高,初晶形核过冷度减小.以牛顿传热方程和热力学理论为基础,结合铝硅合金热分析曲线,可推导出液态合金凝固过程中固相分数,固相生长速度,固相生长加速度的方程,为铝硅合金热分析的研究提供了理论基础.利用金属形核与生长过程中固相生长加速度值,可从理论上解释采用TEG,△T,△TE,t3等作为评估细化及变质结果的热分析判据的原因.     

铸造亚共晶Al-Si合金显微组织中α枝晶相的定量分析

采用金相显微镜和图像分析仪的定量测试技术,计算了亚共晶铝合金中α枝晶相的参数,包括α相的含量、晶粒度和圆整度等。结果表明,经过变质处理后,当α枝晶相的含量较高时,其分布较均匀,晶粒度细化至31μm,圆整度达到1.45。说明图像分析仪能对显微组织中α枝晶相的特征参数进行定量分析,为变质处理工艺的制定打下良好的基础。     

电流对过共晶Al-Si合金凝固组织的影响

在ZL102合金凝固过程中施加电流处理,研究电流对凝固组织的影响规律。结果表明,随着电流的增大,试样底部硅相的富集加剧,而且初生硅的形貌发生改变;当电流增大到50 A,凝固趋向于平衡;随着通电时间的延长,底部硅的富集减弱,组织有一定程度的粗化。     

Solidification kinetics of a near eutectic Al-Si alloy, unmodified and modified with Sr

The purpose of this work was to explore the differences in solidification kinetics between unmodified and Sr modified eutectic Al-Si alloy as revealed by Fourier Thermal Analysis (FTA) and grain-growth kinetics characterization. Thermal analysis were performed in cylindrical stainless steel cups coated with a thin layer of boron nitride, using two type-K thermocouples connected to a data acquisition system. Grain growth kinetics characterization was carried out using solid fraction evolution and grain density data. FTA results for the non modified and modified alloys suggest that there are changes in the solidification rate during eutectic nucleation followed, during growth, by similar solidification rate evolutions, suggesting that this parameter is governed principally by the heat extraction conditions. On the other hand the change of the grain growth parameters estimated for the experimental probes suggest that the presence of Sr may modify the relationship between grain growth rate and undercooling in eutectic Al-Si.     

Cu含量对压铸铝硅合金组织和性能的影响

为研究Cu含量对压铸铝硅合金组织和性能的影响,采用光学显微镜(OM)、扫描电镜(SEM)和能谱仪(EDS)观察了显微组织形貌,并进行了相成分分析。结果表明：A356合金压铸组织中主要是条片状的Si相,添加Cu后,合金中出现Al2Cu相,该相分布在Si相四周及晶界上;随着Cu含量的升高,Si相由条片状变为团聚的骨骼状,除主要强化相Al2Cu相以外,还生成了强化相W相(AlxMg5Si4Cu4);向压铸合金中添加Cu后,合金强度得到了较明显提升,但Cu过高会明显降低合金的塑性。     

Role of bismuth on solidification,microstructure and mechanical properties of a near eutectic Al-Si alloys

Computer aided thermal analysis and microstructural observation showed that addition of bismuth (Bi) within the range of 0.25 and 2 wt% produced a greater effect on the Al-Si eutectic phase than on primary aluminium and Al₂Cu phases. Results showed that with addition of 1 wt% Bi the eutectic silicon structure was refined from flake-like morphology into lamellar. Bi refines rather than modifies the Si structure and increases the Al-Si eutectic fraction solid and more significantly there was no fading even up to 180 min of melt holding. Transmission electron microscopy study showed that the Si twin spacing decreased from 160 to 75 nm which is likely attributed to the refining effect of Bi. It was also found that addition of 1 wt% Bi increased the tensile strength, elongation and the absorbed energy for fracture due to the refined eutectic silicon structure.     

近液相线铸造Al-Si合金浆料非枝晶组织的形成与演变

通过对比实验的方法,利用多次抛光原位观察和金相分析对近液相线铸造Al-Si合金浆料非枝晶组织的形成及演变规律进行研究,进而从熔体结构角度探讨非枝晶组织形成和稳定存在的机制。结果表明:对于Al-7.97Si工业用铝合金,在390~400℃的热环境中,常规近液相线铸造半固态浆料的转移及流变成形时间约为15 s;而在液相线以上不高温度区间对熔体施加旋转磁场作用,可延长浆料转移及流变成形的时间,其主要原因是旋转磁场对过热熔体产生的扰动作用一直影响到凝固过程的形核与长大,一方面使熔体中原子集团的尺寸、形状及分布发生改变,为提高形核率创造了条件,另一方面使固-液界面前沿的溶质浓度梯度减小,抑制成分过冷,同时增大了晶核稳态球形长大的临界半径。     

Mechanics of the die coating application in the permanent mould casting process

The present study is intended to provide a basis for the practical implementation of shop-floor monitoring and control of an operation which, in the production sequence, accounts most for the variability of the permanent mould casting process. After describing the purpose and nature of the coatings applied on permanent mould cavities, their expected functional properties were analysed. The physical parameters governing the spray process have been isolated and their relation to the thickness of the coating deposit derived. The covering capability of the spray process in the early stage of the operation has been studied. Experimental observations are presented for two commercial coatings of widely different properties and usage. Finally, spray gun handling has been shown to affect the uniformity of the coating thickness along with the aspect ratio of the spray cone.     

铝硅合金压铸模镶块与型芯“等寿命设计”的实验研究

如何保证铝硅合金压铸模的镶块与型芯具有基本相等的使用寿命，从而提高整体模具的寿命，是压铸行业普遍关注的研究课题。作者对铝硅合金压铸模的镶块与型芯的失效形式及选材与热处理工艺规范、压铸工艺参等对其寿命的影响进行了生产实验研究，给出了压铸模镶块与型芯的等寿命设计方案。生产应用表明，本文提供的等寿命设计方案，可以稳定地保持压铸模整体寿命达到10万模次以上，达到了国内先进水平。     

亚共晶Al-Si合金共晶团的形核与生长

采用光学显微镜、扫描电镜及电子背散射衍射技术研究亚共晶Al-Si合金共晶团的形核与生长。通过揭示共晶团和结晶位向的分析发现：在同一个共晶团中Si相和Al相都不是单晶体,而是由不同位向的小＂晶粒＂构成的。提出不能依据共晶团中Al相与周围初生枝晶Al相的位向关系来确定共晶的形核模式的建议。然而,初生枝晶铝相的演化显著影响随后的共晶形核与生长。涉及的杂质元素使共晶Si的形貌由粗大的片状转变成细小的纤维状的变质行为,可能与共晶的形核无关。     

不等壁厚带台阶锥形件冲压成形工艺与模具设计

分析了不等壁厚带台阶锥形件的冲压成形工艺,介绍了有色金属变薄拉深毛坯直径计算方法,采用合适的润滑剂及润滑方法和确定合理的模具间隙,经过多次拉深、变薄拉深和锥部拉深,成形出了表面质量理想的不等壁厚带台阶锥形件。     

Effect of the temperature gradient,growth rate,and the interflake spacing on the microhardness in the directionally solidified Al-Si eutectic alloy

An alloy of composition Al-12.6 wt.% Si was prepared using metals of 99.99% purity. Weighed amounts of aluminium and silicon were melted in the vacuum-melting furnace. This irregular eutectic alloys were directionally solidified upward with a constant growth rate V (8.3×10⁻³ mm/s) and different temperature gradients G (2.0–7.8 K/mm) and also with a constant temperature gradient G (7.8 K/mm) and different growth rates V (8.3–498.7×10 ⁻³mm/s) in the directional solidification furnace. The interflake spacings λ and microhardness H_V were measured from both transverse section and longitudinal section of the specimen. The variations of H_V with respect to G, V, and λ have been determined by using the linear regression analysis method. It has been shown that H_V increases with the increasing values of G and V. On the other hand H_V values decreases with the increasing λ values. The Hall-Petch type relationships obtained in this work have been compared with the previous works.     

强磁场对Al-Si合金中共晶硅生长的影响

对亚共晶Al-6%Si合金进行钠盐变质处理后,分别在不施加与施加强磁场的条件下,在液相区740℃、固液两相区590℃和固相区470℃三个温度,使合金快速冷却,观察到了共品硅的不同生长过程.磁感应强度B=0T时,共晶硅由短小的层片状至较长的层片状直至尖锐的纤维状;B=10T时,共晶硅由细小的弥散分布至复杂的丛簇状直至圆钝的颗粒状.即施加强磁场町以改变共晶硅的生长形态.