热挤压变形对搅拌铸造SiCp/2024复合材料显微组织与力学性能的影响

利用搅拌铸造?热挤压工艺制备SiCp/2024复合材料板材。通过金相观察(OM)、扫描电镜(SEM)及力学性能测试等手段研究了该复合材料热挤压变形前后的显微组织与力学性能。结果表明,复合材料铸坯主要由大小为80μm~100μm的等轴晶组成,晶界第二相粗大呈非连续状分布,SiC颗粒较均匀地分布于基体合金,大部分SiC颗粒沿晶界分布,少数颗粒分布于晶内;热挤压变形后,显微孔洞等铸造缺陷和SiC颗粒团聚现象明显消除,SiC颗粒及破碎的第二相沿热挤压方向呈流线分布,复合材料的强度和塑性显著提高;拉伸断口表明,热挤压变形有利于改善SiC颗粒与基体合金的界面结合;SiCp/2024复合材料主要的断裂方式为SiC颗粒断裂和SiC/Al的界面脱粘。     

Microstructure and wear performance of Al5083/CeO2/SiC mono and hybrid surface composites fabricated by friction stir processing

Friction stir processing (FSP) was utilized to produce surface composites by incorporating nano-sized cerium oxide (CeO₂) and silicon carbide (SiC) particles individually and in combined form into the Al5083 alloy matrix. The study signified the role of these reinforcements on microstructure and wear behavior of the resultant surface composite layers. The wear characteristics of the resultant mono and hybrid surface composite layers were investigated using a pin-on-disc wear tester at room temperature. The microstructural observations of FSPed regions and the worn out surfaces were performed by optical and scanning electron microscopy. Considerable grain refinement and uniform distribution of reinforcement particles were achieved inside the nugget zone. All the composite samples showed higher hardness and wear resistance compared to the base metal. Among the composite samples, the hybrid composite (Al5083/CeO₂/SiC) revealed the highest wear resistance and the lowest friction coefficient, whereas the Al5083/SiC composite exhibited the highest hardness, i.e., 1.5 times as hard as that of the Al5083 base metal. The enhancement in wear behavior of the hybrid composites was attributed to the solid lubrication effect provided by CeO₂ particles. The predominant wear mechanism was identified as severe adhesive in non-composite samples, which changed to abrasive wear and delamination in the presence of reinforcing particles.     

WC_p/2024Al基复合材料的腐蚀机理

采用动电位阳极极化法对体积分数为11.4%WCp/2024Al基复合材料及其基体合金在3.5%NaCl水溶液中的耐蚀性能进行研究。结果表明,由于WC颗粒的加入,提高了WCp/2024Al基复合材料的腐蚀速度。通过对恒电位极化后试样观察发现,WCp/2024Al基复合材料腐蚀机理为富Cu相作为阴极区与其周围的贫Cu区作为阳极区构成电偶腐蚀以及WC颗粒与基体间的协同腐蚀作用。这种双重的电偶腐蚀致使复合材料腐蚀速度加快。     

Effects of SiC Particle Size and Process Parameters on the Microstructure and Hardness of AZ91/SiC Composite Layer Fabricated by FSP

In this study, friction stir processing (FSP) was employed to develop a composite layer on the surface of as-cast AZ91 magnesium alloy using SiC particles (5 μm and 30 nm). The effects of the rotational and traverse speeds and the FSP pass number on the microstructure and microhardness of the friction stir processed (FSPed) layer with and without SiC particles were investigated. Optical microscopy and scanning electron microscopy (SEM) were employed for microstructural analysis. FSP produces a homogeneous microstructure by eliminating the precipitates near the grain boundaries. The analyses showed that the effects of the rotational and traverse speeds on the microstructure of specimens produced without nano-sized SiC particles are considerable; however, they are negligible in the specimens with particles. While the second FSP pass enhances the microstructure and microhardness of the samples with SiC particles, it has no significant effect on such properties in the samples without SiC particles.     

SiCp/2024Al基复合材料的点蚀行为

采用动电位阳极极化法对17%SiCp/2024Al基复合材料及其基体合金在3.5%NaCl水溶液中的耐蚀性进行了研究.结果表明:SiC颗粒的加入并不影响SiCp/2024Al基复合材料的点蚀敏感性,但与基体相比,其耐蚀性有所下降.对极化后和长期浸泡试样的腐蚀形貌观察发现:与基体相比,SiCp/2024Al基复合材料表面上的蚀孔数量相对较多,蚀孔尺寸稍小,大小分布不均匀;最大蚀孔较深,并有严重的裂缝腐蚀;裂缝腐蚀的存在会使SiCp/2024Al基复合材料的点蚀抗力明显降低.能谱分析表明:SiCp/2024Al基复合材料的腐蚀机制为富Cu阴极相与贫Cu阳极相间的电偶腐蚀,另外,SiC与Al间也存在电偶腐蚀倾向.     

Effect of SiC particles on microstructure and mechanical property of friction stir processed AA6061-T4

Friction stir processing of AA6061-T4 alloy with SiC particles was successfully carried out.SiC particles were uniformly dispersed into an AA6061-T4 matrix.Also SiC particles promoted the grain refinement of the AA6061-T4 matrix by FSP.The mean grain size of the stir zone (SZ) with the SiC particles was obviously smaller than that of the stir zone without the SiC particles.The microhardness of the SZ with the SiC particles reached about HV80 due to the grain refinement and the distribution of the SiC particles.     

Effect of Tool Rotation Speed on Microstructure and Microhardness of Friction-Stir-Processed Cold-Sprayed SiCp/Al5056 Composite Coating

SiC-particle-reinforced Al5056-matrix composite coatings were deposited onto Al2024 substrates by cold spraying using a powder mixture having 15 vol.% SiC. To investigate the effects of friction stir processing (FSP) parameters on the microstructure and microhardness of the as-sprayed coating, the as-sprayed composite coating was then subjected to FSP using a stir tool having a threaded pin with rotation speed of 600 rpm and 1400 rpm. Results showed that the coatings presented Al and SiC phases before and after FSP treatment, and no other diffraction peaks were detected. Fine grains were produced in the Al5056 matrix due to severe plastic deformation during FSP, and the refined SiC particles exhibited a homogeneous distribution in the FSPed coating. In addition, an evident reduction of porosity (from 0.36% to 0.08% at 600 rpm or 0.09% at 1400 rpm) occurred, and a dramatic size reduction of the reinforcement from 12.5 µm to 6.5 µm at 600 rpm or 7.0 µm at 1400 rpm was achieved. Nevertheless, the microhardness profile presented general softening and a decrease from 143.9 HV to about 110 HV.     

Microstructural modification of cast Mg alloys by friction stir processing

Abstract

Cast Mg alloys were processed using friction stir processing (FSP) to acquire a fine grained structure and high strength. Actually, FSP is a novel grain refinement method for light metal alloys. Using FSP, a cast microstructure with coarse grain size was refined to equiaxial fine grain through dynamic recrystallisation; second phase particles were finely dispersed by FSP. Moreover, FSP is effective to eliminate cast defects such as microshrinkages or porosities. Commercial die cast Mg alloy (AZ91D) and high strength Mg–Y–Zn alloy plates were prepared for FSP. Heat input using a rotational tool during FSP closely affected the microstructure in the stirred zone. Actually, FSP with lower heat input produced a finer grain size and higher hardness. Changes in the friction stir processed microstructures affecting mechanical properties were not only grain refinement, but also second phase particle distributions. Results show that alloys with high hardness by FSP have finely dispersed second phase particles without dissolution during FSP.     

Surface modification of aluminium by friction stir processing

In this study, SiC particles were incorporated by using Friction Stir Processing (FSP), into the commercially pure aluminium to form particulate surface layers. Samples were subjected to the various tool rotating and traverse rates with and without SiC powders. Microstructural observations were carried out by employing optical microscopy of the modified surfaces. Mechanical properties like hardness and plate bending were also evaluated. The results showed that increasing rotating and traverse rate caused a more uniform distribution of SiC particles. The hardness of produced composite surfaces was improved by three times as compared to that of base aluminium. Bending strength of the produced metal matrix composite was significantly higher than processed plain specimen and untreated base metal.     

搅拌铸造SiC_p/2024铝基复合材料的显微组织与力学性能

利用搅拌铸造?热挤压工艺制备SiCp/2024铝基复合材料板材,研究该复合材料铸态、热挤压态和热处理态的显微组织及力学性能。结果表明:SiC颗粒较均匀地分布于铸锭中,大部分SiC颗粒沿晶界分布,少数颗粒分布于晶内,晶界粗大的第二相呈非连续状分布;复合材料经热挤压变形后,显微孔洞等铸造缺陷明显消除,破碎的晶界第二相及SiC颗粒沿热挤压方向呈流线分布,复合材料的强度和塑性显著提高;对热挤压板材进行(495℃,1h)固溶处理+(177℃,8h)时效处理后,其抗拉强度达430MPa,此时的主要析出强化相为S′(Al2CuMg);热挤压变形有利于改善SiC颗粒与基体合金的界面结合,热处理SiCp/2024铝基复合材料的主要断裂方式为基体合金的延性断裂、SiC颗粒断裂和SiC/Al的界面脱粘。     

镁合金表面搅拌摩擦原位复合材料化的新方法

为了解决搅拌摩擦加工在进行复合材料制备过程中增强相需预置,及在基体中分布不均的问题,提出表面搅拌摩擦原位复合材料化的新方法.利用搅拌头在轧制态AZ31镁合金板材上进行表面复合材料制备,并对制备的复合材料进行显微观察、微观硬度测试、表面耐磨度测试.结果表明,相较于预置搅拌摩擦加工制备复合材料的方法,文中方法能够使增强相在基体中分布更加弥散、均匀,从而进一步提高复合材料层的显微硬度,以及材料表面的耐磨度,同时简化了搅拌摩擦加工制备复合材料的工艺过程.     

酸性盐雾下2024铝合金搅拌摩擦焊接头的腐蚀行为

在详细分析2024铝合金搅拌摩擦焊焊缝表面微结构的基础上,采用酸性连续盐雾试验研究焊缝表面的腐蚀行为。组织分析表明,焊缝表层因受搅拌头轴肩水平挤压作用而呈现弧形条纹特征,并导致晶粒和第二相粒子得到显著细化;合金中的第二相粒子主要为棒状的Al₂CuMg（S相）和颗粒状的CuAl₂（θ相）。盐雾试验表明,搅拌摩擦焊焊缝区耐蚀性因包铝层遭到破坏而呈现下降趋势,腐蚀程度因焊缝表面残留的纯铝而呈现不均匀性。腐蚀首先从局部点蚀开始,最终演变为剥落腐蚀。     

搅拌摩擦加工制备A356铝基复合材料的显微组织与力学性能(英文)

通过搅拌摩擦加工技术将SiC颗粒加入到A356铝合金中制备铝基复合材料,搅拌摩擦加工参数为:旋转速度1800r/min和行进速度127mm/min。基体金属A356铝合金为亚共晶AlSi枝晶组织,而搅拌区的组织与基体金属区不同。共晶Si和SiC颗粒均匀分布于初始铝固溶体中,而经历了剧烈变形的热力影响区的共晶Si和SiC颗粒呈沿旋转方向分散的特征。搅拌区的硬度比基体金属的高,因为在搅拌区存在的缺陷明显减少,共晶Si和SiC均匀分布在其中。     

Corrosion behavior of SiC reinforced magnesium composites

The corrosion behavior of two SiC reinforced Mg-based metal matrix composites, Mg-6SiC and Mg-16SiC (in volume percent), has been studied in freely aerated 1 M NaCl solution and compared with that of pure Mg. The presence of SiC particles deteriorated the corrosion resistance of magnesium. Corrosion resistance decreased with increasing SiC volume fraction. The galvanic corrosion current density between pure SiC and pure Mg has been experimentally measured using zero resistance ammeter technique and theoretically determined using mixed potential theory. Galvanic corrosion between Mg matrix and SiC reinforcement in the composites did not contribute significantly to the overall corrosion rate. Electrochemical impedance spectroscopy indicated that the higher corrosion rates for the composites could be related to the defective nature of surface film.     

Modelling the corrosion behaviour of Al2CuMg coarse particles in copper-rich aluminium alloys

The corrosion behaviour of 2024 aluminium alloy in sulphate solutions was studied; attention was focused on the influence of coarse intermetallic Al₂CuMg particles on the corrosion resistance of the alloy. Model alloys representative of the aluminium matrix and of Al₂CuMg coarse intermetallics were synthesized by magnetron sputtering. Open-circuit potential measurements, current-potential curve plotting and galvanic coupling tests were performed in sulphate solutions with or without chlorides. Further explanations were deduced from the study of the passive films grown on model alloys in sulphate solutions. The results showed that model alloys are a powerful tool to study the corrosion behaviour of aluminium alloys.     

SiC_p/2024Al复合材料阳极氧化膜耐蚀性的电化学阻抗研究

采用电化学阻抗技术研究了碳化硅颗粒增强 ２０２４铝基复合材料（ＳｉＣｐ／２０２４Ａｌ）硫酸阳极氧化膜在 ３．５％ＮａＣｌ水 溶液中的耐蚀性;作为比较,对 ２０２４ Ａｌ的阳极氧化膜耐蚀性也进行了研究 结果表明,ＳｉＣｐ／２０２４Ａｌ复合材料的阳极氧化膜 具有良好的耐 ＮａＣｌ溶液腐蚀的能力,而且重铬酸盐封闭比热水封闭的阳极氧化膜耐蚀性更好．由于氧化膜中出ＳｉＣ颗粒的存在破 坏了氧化膜的完整性和均匀性,故复合材料阳极氧化膜的耐蚀性不如 ２０２４ Ａｌ合金．     

Investigations on the corrosion behaviour and biocompatibility of magnesium alloy surface composites AZ91D-ZrO2 fabricated by friction stir processing

In the current study, friction stir processing was applied as a methodology to produce surface composites of AZ91D magnesium alloy with ZrO₂ particles. Microstructural evolution, microhardness profile and corrosion behaviour of the developed surface composite were analysed. The results indicate that the combined effect of friction stir processing and reinforcement of ZrO₂ reduced the grain size, and fragmented and dispersed the secondary phases. The fine dispersion of ZrO₂ particles contributed to the enhancement of cumulative surface potential, and hence the corrosion resistance of the developed surface composite. The analysis of post-corrosion test specimens revealed the formation of corrosion products that had similar composition to that of hydroxyapatite. The formation of such corrosion products is beneficial, as it contributes to corrosion resistance (stable and adherent layer) and biocompatibility.     

Effect of process parameters on corrosion rate of friction stir welded aluminium SiC–Gr hybrid composites

Abstract

In the present study, the influence of processing parameters of friction stir welding on the corrosion rate of the welded joints of aluminium SiC–Gr hybrid composites was investigated. The experimental results indicate that the corrosion resistance of the welded joints increases at high welding (traverse) speed and/or low values of rotational speed. These variations occur as a result of the changes in the joint microstructure, where fine grains are developed as a consequence of a relatively low heat input and fast cooling to room temperature by ambient air associated with low rotational speed and/or high welding speeds. The mixed electrode theory is used to explain these variations of the corrosion rate, where the area ratio of cathode/anode for the galvanic couple between the aluminium metal matrix and the reinforcement constituents becomes small for fine grains. Thus, the corrosion resistance of the welded joints is increased.     

Effect of friction stir processing tool probe on fabrication of SiC particle reinforced composite on aluminium surface

Abstract

An investigation has been carried out of the effects of tool probe shape and size on the formation of surface composite by uniformly distributing SiC particles into a surface layer of an A1050-H24 aluminium plate through friction stir processing (FSP). Tool probes of three different diameters (3, 5 and 7 mm) and four different shapes (circular with threads, circular without threads, square and triangular) have been used to fabricate the surface layers at rotation speeds of 1500–2250 rev min^?1 and a travelling speed of 1·66 mm s^?1. The SiC particles were packed into a groove of 3 mm width and 1·5 mm depth cut on the aluminium plate and covered by an aluminium sheet of 2 mm thickness. A rotating tool was plunged into the plate through the cover sheet so that the tip of the probe reached beyond the bottom of the groove. As a result, it was found that the square probe dispersed the SiC particles homogeneously in the nugget zone compared with other probe shapes regardless of the rotation speeds. Furthermore, the distributed particles and also the aluminium matrix grain size became finer by the use of square probe than those of the other shapes. On the other hand, the wear rates of the square and triangular probes were higher than that of circular shape. The worn iron debris from the tool reacted with aluminium matrix and form fine iron aluminides compound dispersed in the nugget zone. The probe size had limited effects on the homogeneity of the SiC particles distribution in the nugget zone; the distribution of SiC particles obtained by triple FSP passes was less homogeneous when the probe size was smaller. Microhardness of the nugget zone was homogeneously increased to a level as high as 60 HV with tool of square probe shape after three passes to be compared with 23 HV of the aluminium matrix beside the nugget zone.     

Influence of addition of Grp/Al2O3p with SiCp on wear properties of aluminum alloy 6061-T6 hybrid composites via friction stir processing

Aluminum alloy base surface hybrid composites were fabricated by incorporating with mixture of (SiC+Gr) and (SiC+Al₂O₃) particles of 20 μm in average size on an aluminum alloy 6061-T6 plate using friction stir processing (FSP). Microstructures of both the surface hybrid composites revealed that SiC, Gr and Al₂O₃are uniformly dispersed in the nugget zone (NZ). It was observed that the addition of Gr particles rather than Al₂O₃ particles with SiC particles, decreases the microhardness but immensely increases the dry sliding wear resistance of aluminum alloy 6061-T6 surface hybrid composite. The observed microhardness and wear properties are correlated with microstructures and worn micrographs.