Effect of Sr modification on microstructure and thermal conductivity of hypoeutectic Al−Si alloys

Trace amount of Sr(0.05 wt.%)was added into the hypoeutectic Al−Si(3−12 wt.%Si)alloys to modify their microstructure and improve thermal conductivity.The results showed that the thermal conductivity of hypoeutectic Al−Si alloys was improved by Sr modification,and the increment and increasing rate of the thermal conductivity gradually increased with Si content increasing.The improvement of thermal conductivity was primarily related to the morphology variation of eutectic Si phases.In Sr-modified Al−Si alloys,the morphology of eutectic Si phases was a mixed morphology of fiber structure and fine flaky structure,and the proportion of the fine flaky eutectic Si phases gradually decreased with Si content increasing.Under the Si content reaching 9 wt.%,the proportion of fine flaky eutectic Si phases was nearly negligible in Sr-modified alloys.Correspondingly,the increment and increasing rate of thermal conductivity of Sr-modified alloys reached the maximum and tended to be stable.

Modification and refinement mechanism of Mg_2Si phase in Sr-containing AZ61-0.7Si magnesium alloy

The effect of Sr on modification and refinement of the Mg 2 Si phase in an AZ61-0.7Si magnesium alloy has been investigated and analyzed.The results indicate that Sr can effectively modify and refine the Chinese-script shaped Mg2Si phase in the AZ61-0.7Si alloy.By adding 0.06wt.%-0.12wt.%Sr to AZ61-0.7Si alloy,the Mg2Si phase in the alloy can be changed from the initial coarse Chinese-script shape to fine granule and/or irregular polygonal shapes.Accordingly,the Sr-containing AZ61-0.7Si alloy exhibits higher tensile and creep properties than the AZ61-0.7Si alloy without Sr modification.The mechanism on modification and refinement of the Mg2Si phase in Sr-containing AZ61-0.7Si alloy is possibly related to the following two aspects:(1)adding Sr may form the Al4Sr phase which can serve as the heterogeneous nucleus for the Mg2Si particles and/or(2)adding Sr may lower the onset crystallizing temperature and increase the undercooling level.

Effects of Solution Treatment Time and Sr-Modification on Microstructure and Mechanical Property of Al-Si Piston Alloy

The purpose of this paper was to investigate the effects of solution treatment time and Sr-modification on the microstructure and property of the Al-Si piston alloy.It was found that as-cast microstructures of unmodified and Sr-modified Al-Si alloys consisted of a coarse acicular plate of eutectic Si,Cu_3NiAl_6 and Mg_2Si phases in theα-Al matrix but different in size and morphology.Both size and inter-particle spacing of Si particles were significantly changed by increasing the solution treatment time.After a short solution treatment,the coarse acicular plate of the eutectic Si appears to be fragmented.Fully modified microstructure of Sr-modified alloy can reduce the solution treatment time compared to unmodified alloy.The maximum of a peak hardness value is found in the very short solution treatment of both Al-Si piston alloys.Compared to 10 h solution treatment,the solution treatment of 2-4 h is sufficient to achieve appropriate microstructures and hardness. The short solution treatment is very useful to increase the productivity and to reduce the manufacturing cost of the Al-Si piston alloys.

Distributions of Sr and Fe and their influence on modification of hypoeutectic Al-Si alloy

The influence of cooling rate and Fe-containing phases on Sr-modification of Si phases in hypoeutectic Al-Si alloys, a problem with great industrial importance, was investigated. The microstructures of samples were examined using scanning electron microscopy(SEM) with energy-dispersive X-ray spectroscopy(EDX). A new method of electron probe microanalysis(EPMA) map scanning was used to analyze the Sr distribution, which gave quantitative results covering more Si particles. EPMA map scanning, together with SEM with EDX, was also used in analyzing the distribution of Fe phases. Results show that Fe-containing phase was related to the unmodified Si particles in samples with partial modification failure and the plate-like Si phases in samples without modification failure. Such a relationship was further confirmed by the microstructure observation.In conclusion, a partial failure of Sr-modification can be caused by both slow cooling rate and Fe-containing phases.

Efficacies of ^(89)Sr and combination treatments with regional extra-beam radiotherapy for cancer patients with multiple bone metastasis

Objective:The aim of the study was to observe the efficacies of 89Sr and combination treatments with regional extra-beam radiotherapy for cancer patients with multiple bone metastasis.Methods:A total of 106 patients were divided into two groups, and each group were 53 patients:the simple 89Sr treatment group (simple group), and local radiotherapy and 89Sr treatment group (combination group).The dose of 4 mci of 89Sr was made in every patient by intravenous injection, 6 MV linear accelerator external irradiation dose was given 30-60 Gy/2-4 weeks.Results:The effective rates of simple and combination groups were respectively 83.01% and 90.56%; the effective improvement rates of the bone focus of two groups were 75.48% and 86.8%, respectively.There was homologous improvement in general conditions.Conclusion:89Sr treatment has a certain effect to the cancers of whole-body multiple bone metastases.And the combined treatment with regional radiotherapy can improve the efficacy and life quality of cancer patients with bone metastasis.

Modification and aging precipitation behavior of hypereutectic AI-21wt.%Si alloy treated by P+Ce combination

In the present study, the tested hypereutectic Al-21wt.%Si alloys were prepared by modifying the melt using different proportions of P and Ce, and then applying T6 heat treatment. The modification effects and mechanism of P＋Ce complex modifier on the Si phase of hypereutectic Al-21wt.%Si alloy were studied, and the aging precipitation behavior after modification was characterized by means of tensile strength measurement, OM, SEM and TEM analysis. The results show that the massive primary silicon phase particles are significantly refined after modification, while the needle-like eutectic silicon crystals become fibrous and short. It was found that the mechanism of phosphorus modification on the primary silicon can be attributed to heterogeneous nucleation of AlP, while the modification mechanism of Ce can be explained by adsorbing-twinning theory. In the aged microstructure of the modified hypereutectic Al-21wt.%Si alloy, there existed some strengthening phases such as AI4Cu9, Al2Cu, AlCu3, and Al57Mn12. The P＋Ce complex modifier not only affected the size of primary silicon and eutectic silicon, but also the aging behavior of alloys under the heat treatment process. When Al-21wt.%Si alloy was modified using 0.08%wt.P ＋ 0.6wt.% Ce, the aging precipitates were dispersed uniformly in the alloy, and its mechanical properties at room and elevated temperatures are optimized （Rm = 287.6 MPa at RT, Rm = 210 MPa at 300 ℃）.

Microstructure and corrosion behavior of Al3Ti/ADC12 composite modified with Sr

In this study, we investigated the effect of the addition of Sr （0wt%, 0. lwt%, 0.2wt%, and 0.3wt%） on the microstaalcture and cor- rosion behavior of A13Ti/ADC12 composite by optical microscopy, X-ray diffraction, sca^lning electron microscopy, mid energy diffraction spectroscopy. The results reveal that the c^-A1 phases were nearly spherical mid 40 gin in size and that the eutectic Si phases became round in the composite when the Sr content reached 0.2wt%. The A13Ti paxticles were distributed uniformly at the grain boundary. The results of the corrosion examination reveal that the A13Ti/ADC12 composite exhibited a minimum corrosion rate of 0.081 g.m 2,hl for an Sr content of 0.2wt%, which is two thirds of that of umnodified composite （0.134 g.m4.h 1）. This improved corrosion resistaalce was due to galvamc cor- rosion, which resulted from the low area ratio of the cathode to anode regions. This caused a low-density corrosion current in the composite, thereby yielding optimum corrosion resistmlce.

轧制改性Pb-Ag-Ca-Sr-RE阳极的电化学和力学性能研究

研究了轧制改性处理Pb-Ag-Ca-Sr-RE阳极的性能,考察了轧制方向、变形量和温度对阳极电阻率的影响,以及不同交叉轧制变形量下的阳极电位、槽电压、电流效率、能耗、腐蚀速率和硬度。结果表明:与轧制温度相比,轧制方向和变形量对阳极电阻率有较大影响。在轧制变形量60%、轧制温度35℃的条件下进行交叉轧制改性的阳极具有最佳综合性能:稳定阳极电位1.296 V,槽电压3.08 V,电流效率91.1%,生产锌的电解能耗2771.43 kW·h/t,腐蚀速率4.8 g/(m^(2)·h),硬度35.4 HV。

DIRECT DIGITAL DESIGN AND SIMULATION OF MESHING IN WORM-GEAR DRIVE

A direct digital design method （DDDM） of worm-gear drive is proposed. It is directly based on the simulation of manufacturing process and completely different from the conventional modeling method. The loaded tooth contact analysis （LTCA） method is analyzed, in which the advanced surface to surface searching technique is included. The influence of misalignment errors and contact deformations on contact zone and transmission error （TE） is discussed. Combined modification approach on worm tooth surface is presented. By means of DDDM and LTCA, it is very conven- ient to verify the effect of worm-gear drive＇s modification approach. The analysis results show that, the modification in profile direction reduces the sensitivity of worm-gear drive to misalignment errors and the modification in longitudinal direction decreases the TE. Thus the optimization design of worm-gear drive can be achieved prior to the actual manufacturing process.

Al-Sr-La中间合金改性对A356铝合金组织和性能的影响

采用Al-Sr-La中间合金对A356铝合金进行改性处理,研究了Sr和La对A356铝合金微观结构和力学性能的协同变质机制。结果表明:添加0.5 mass%的Al-Sr-La中间合金对A356铝合金的改性效果最佳,此时A356铝合金具有优良的显微组织与力学性能,其α-Al相的晶粒细小,二次枝晶臂间距(SDAS)降低至14.2μm,较未改性的A356铝合金降低了36.6%,针状共晶Si转变为蠕虫状共晶Si,平均晶粒尺寸减小至0.86μm。与未改性的A356铝合金相比,添加0.5 mass%的Al-Sr-La中间合金改性后,合金的抗拉强度增加了22.4%,屈服强度增加了11.1%,伸长率增加了89.7%。最后,在实验结果的基础上,结合凝固理论,研究了Sr和La的协同变质机制。Sr吸附于Si相生长界面上,产生孪晶平面,抑制Si相的生长,使得Si以孪晶凹谷机制生长,实现对共晶Si的改性;La则由于Sr对Si的作用,使得La在共晶Si的凹槽处聚集,阻碍了Si的生长,改善共晶Si的形貌。

MODIFICATION EFFECT OF Sr ON Al-Si ALLOYS

By inserting the single crystal silicon seeds into Sr modified Al-22wt-% Si alloy melts,the fact that nucleation and growth of Si-phase are affected by Sr addition has been confirmed.It is suggested that this effect is caused by the adsorption of Sr on{111}_(si),and the modification of eutectic structure results from the variation of leading phase in the eutectic from Si to α-Al.

Sr及RE变质对砂型铸造ZL114A合金组织及力学性能的影响

采用20和40 mm厚的ZL114A两种试样,对比研究了稀土变质和锶变质对砂型铸造ZL114A合金试样力学性能和组织的影响。结果表明:不变质、稀土变质和锶变质等三种方案的试样抗拉强度差异较小(在5%以内),而伸长率差异较大。锶变质后的试样(T6状态)伸长率最高,比其它两种方案高出28%以上。通过对比三种方案伸长率最小的试样组织发现,锶变质试样的共晶硅组织细化最明显,且试样聚集性的孔洞类缺陷又较少,这对试样的伸长率提升有很大作用。稀土变质后的试样组织中会形成一些树枝状或片层状化合物Al REMg Si相,且聚集性的孔洞类缺陷较多,这类组织反而降低了试样的伸长率。

RE、Sr变质对AHS-2铝合金组织及性能的影响

研究了RE、Sr、RE+Sr不同变质处理AHS-2铝合金铸态显微组织变化.实验结果表明:当RE0.1%+Sr0.3%复合变质AHS-2合金时,其组织中的初生α-Al发生明显细化,形貌呈细小圆球状等轴晶,尺寸约为20~30μm,且分布均匀,共晶硅晶粒细小,合金得到良好的变质细化效果.

P、Sr、RE变质对过共晶Al-Si合金组织形态的影响

采用P、Sr、混合RE对含Si量22%～26%的过共晶铝硅合金进行变质处理,利用金相显微镜分析了单一元素变质及复合变质对合金初晶硅和共晶硅组织形态的影响。结果表明,P为初晶硅变质元素,Sr为共晶硅变质元素,RE能同时细化初晶硅和共晶硅;试验发现Sr虽然不能细化初晶硅,但对初晶硅有明显的裂解作用;P和RE复合变质使得初晶硅尺寸减小到25μm,而加入Sr后,由于Sr对初晶硅的裂解作用,使得初晶硅的尺寸减小到15μm,共晶硅大部分呈蠕球杆状或团球状,均匀弥散分布;试验得到了一种初晶硅和共晶硅细化效果均良好的复合变质剂。

Al-P-RE-Sr复合变质过共晶铝硅合金

研究了A l-P-RE-Sr复合变质剂对A l-30%S i合金组织的影响。经变质处理后,可使初晶硅长时间成弥散状态,不发生聚集,平均尺寸不超过35μm,同时共晶硅也被细化成纤维状或点状,变质长效性可达7 h以上。变质后石墨型与金属型浇注对变质效果的影响无太大区别。材料的力学性能也得到了提高,抗拉强度达到234.3MPa,伸长率达3.0%。

新型Al-Sr-RE复合细化变质剂及其在ZL102合金中的作用

研制了一种新型、高效的Al Sr RE复合细化变质剂 ,该合金熔点较低 (6 39 2～ 740℃ ) ,变质潜伏期短(≤ 10min) ,变质能力强 ,变质效果好 ,并且可以显著细化Al Si合金枝晶组织 ,与工业用Al 10Sr、Al 8.7Sr 2 .8Ti 0 2B合金相比 ,该合金使ZL 10 2合金的二次枝晶间距减小了 2 2 6 %～ 2 3 2 %。

Sr+RE在Al-40wt%Si合金中的复合变质作用

研究了Sr+RE复合变质对Al-40wt%Si合金的组织和性能的影响。结果表明,Sr+RE复合变质处理不仅对初晶硅和共晶硅具有变质作用,对枝晶α也有明显的细化作用。当RE加入量保持不变,随着Sr加入量的增加,初晶硅由角块状或大板片状先变为小块状再变为多角的大块状,边、角钝化;共晶硅由针片状变为纤维状加短杆状,最后为密实短杆状,甚至粒状;枝晶α由高度发达的树枝状转变为等轴晶,分布均匀。另外,随Sr加入量的增加,合金力学性能得到显著提高,抗拉强度提高37%,伸长率增加1倍多,硬度提高21%;当Sr加入量为0.05wt%～0.077wt%时,组织形貌最理想,综合力学性能最优。

Al-P-RE-Sr复合变质过共晶铝硅合金

研究了Al-P-RE-Sr复合变质工艺对Al-30%Si合金中初生硅和共晶硅的细化效果。复合变质处理后,可同时细化初生硅和共晶硅,使初晶硅长时间成弥散状态,不发生聚集,平均尺寸不超过35μm,同时共晶硅也被细化成纤维状或点状,变质长效性可达7h以上;材料的力学性能也得到了提高,抗拉强度达到234.3MPa,伸长率达到3.0%。

Sr、B和RE复合变质对Al-30Si合金组织和性能的影响

研究Sr、B和RE复合变质对Al-30Si合金组织与性能的影响。结果表明,细化变质处理后的合金组织形貌发生了显著变化,α(Al)相枝晶群消失,转变为等轴晶或柱状晶;初晶硅颗粒细化,棱角钝化;针状的共晶硅变成短杆状或颗粒状,分布均匀。合金抗拉强度提高55%,伸长率增加约66%,硬度略有增加。当RE含量为0.5%～0.8%时,合金表现出较好的综合力学性能。

P-Sr-RE复合变质对过共晶铝硅合金微观组织的影响

通过单独添加稀土元素和复合添加磷+锶+稀土研究两种变质剂对Al-25%Si合金的变质效果,再经重熔和选择不同模具研究变质剂的重熔性和冷却速度对变质效果的影响。结果表明:稀土元素的添加可同时实现对初晶硅和共晶硅的细化变质,当稀土加入量为0.8%时,初晶硅平均尺寸为45μm,共晶硅细化为颗粒状或短棒状。RE加入量为1.0%,锶加入量为0.8%,磷加入量为0.8%时,初晶硅平均尺寸为33μm,共晶硅为颗粒状或短棒状。P-Sr-RE复合变质时,具有很好重熔性能,重熔5次后,初晶硅平均尺寸均小于60μm,共晶硅平均尺寸均小于10μm。此外,变质效果受冷却速度的影响很小,不同模具浇注后合金的初晶硅平均尺寸均小于33μm,共晶硅均为细小的短棒状。