On using mixtures of liquids for ultrasonic cleaning

Abstract

The effects of mixing various liquids on the acoustic properties of the resultant mixtures are discussed. These properties are ultrasonic radiation pressure that induces the agitation of liquids in ultrasonic cleaners and ultrasonic cavitation. Both these physical phenomena are direct causative agents of ultrasonic cleaning.     

Effects of sonoprocessing on microstructure and mechanical properties of A390 aluminium alloy

Abstract

Ultrasound is defined in terms of human hearing and it is a sound having a frequency higher than that to which the human ear can respond. The attempts to use the ultrasound at casting process have been carried out and there are a lot of study results on grain refinement on microstructure of casting alloys. However, these studies almost have been focused on mould vibration at solidifying melts of solid and liquid coexistence temperature. In this study, high intensity ultrasound was injected in aluminium full melts, especially A390 alloy, to evaluate the effect of ultrasound on microstructure and mechanical properties of castings. The effect of ultrasonic injection on melts could be summarised as follows: reduction of mean size of primary silicon, variation of phase distribution, improvement of solute homogeneity and mechanical properties.     

Magnesium matrix nanocomposites fabricated by ultrasonic assisted casting

Abstract

Magnesium matrix composites reinforced with nano-sized SiC particles (n-SiC_p/AZ91D) were fabricated by high intensity ultrasonic assisted casting. The microstructure of the nanocomposites was investigated by optical microscopy, scanning electronic microscopy (SEM), high resolution transmission electronic microscopy (HRTEM) and Energy Dispersive Spectroscopy (EDS) methods. The results showed that the dispersion and distribution of n-SiC_p in magnesium alloy melts were significantly improved by ultrasonic processing. Compared to the unreinforced AZ91D matrix, mechanical properties of the nanocomposites including tensile and yield strengths were remarkably improved and the yield strength increased by 117% after gravity permanent mould casting.     

Interfacial structure and bond strength of ultrasonic brazed Al–304 stainless steel dissimilar joints

Abstract

A filler alloy (Zn–14 at.-%Al) was used to join aluminium to 304 type stainless steel by ultrasonic brazing at 673 K for different ultrasound application times. Different reaction layers could be observed at the interface, containing Fe–Al, Fe–Zn, and Al–Zn solid solutions. As the amount of these solid solutions increased at the interface, there was a gradual improvement in the joint bond strength. The maximum bond strength of 146 MPa was obtained for the Al–304 joint brazed at 673 K for 3 s ultrasound application time. A critical remaining thickness of the filler alloy after ultrasonic application improves the interfacial joining. Extending the ultrasound application time beyond 3 s causes a bulk escape of the brazing alloy from the interface and leads to a direct interaction between aluminium and 304, which increases the possibility of forming intermetallics, and consequently decreases the joint bond strength.     

超声细化处理AZ80镁合金过程中的声场数值模拟

采用不同强度超声对AZ80镁合金熔体进行处理以改善合金的凝固组织。当施加的超声强度为30.48W/cm2时,合金的平均晶粒尺寸由未经超声处理时的303μm降低为148μm。为了进一步了解超声改善镁合金微观组织的机理,采用数值模拟的方法研究超声声压对空化泡行为的影响,并且对熔体中的超声场分布情况进行分析。结果表明,熔体内不同位置所受的声压是不同的,因此不同位置上的铸锭试样的晶粒细化程度也不同。随着超声强度的增加,声压值增加,而合金的晶粒尺寸则随之降低。     

The effect of focused ultrasound on the electrochemical passivity of iron in sulfuric acid

Focused ultrasound was used to study passivity of pure iron in 2 N H₂SO₄. Ultrasonic waves were used to depassivate a passive surface film and influence the subsequent repassivation process. A curved piezo-electric transducer produced high frequency (1.58 MHz) ultrasonic waves which created cavitation at the focal point. Acoustic focal intensities up to 3.4 kW cm^?2 were generated. Low frequency (20 kHz) ultrasound was produced with a commercial sonicator equipped with an exponential microhorn. At high focal intensities (above 1.5 kW cm^?2) a single (100 ms) pulse of ultrasound produced depassivation; at low intensities continuous ultrasonic exposure was required. In all cases, the induced depassivation was followed by precipitation of a metal salt film upon the metal surface before the oxide film formation.     

Accelerated method for testing soldering tendency of core pins

Abstract

An accelerated method for testing die soldering has been proposed and tested. High intensity ultrasonic vibration has been applied through a core pin to molten aluminium in order to simulate service conditions under die casting. Such conditions include high pressure and high impingement speed of molten metal on the pin. Soldering tendency of H-13 steel pins with or without commercial coatings was tested using this accelerated method. The experimental results indicate that soldering occurs within a few minutes of testing using this new method, much faster than that using the conventional methods. The coating failure mechanism identified in this new method is identical to that observed in the conventional methods, suggesting that the new method is suitable for testing soldering tendency of core pins under die casting conditions.     

Increasing the efficiency of ultrasonic cleaning by means of directed action of an electric field in liquid media

The directed action of an electric field on liquid media at ultrasonic cleaning was investigated. This allowed adjusting the intensity of the cavitation process, accelerating the processes of transport and dissolution of pollutants, and facilitated more effective clearing of products with microrelief surfaces.     

Effect of ultrasonic melt treatment on microstructure of A356 aluminium cast alloys

Abstract

A systematic study of the effect of ultrasonic treatment on the structure of the A356 Al–Si–Mg alloy was carried out. Ultrasonic vibrations were applied to the melt at several temperatures (628 to 608°C) for different periods (0–180 s). The results showed that the ultrasonic treatment is effective in controlling the morphology and size of aluminium grains when applied between 619 to 626°C, and is very effective at 622–625°C, where fine non-dendritic grains are formed. Grain sizes smaller than 60 μm and roundness values of 0˙7 and higher were achieved by 15 s ultrasonic treatment at 623 and 620°C. At higher temperatures, the microstructures are dominantly rosette like and dendritic. At lower temperatures (below 617°C), the samples show inhomogeneous microstructures in terms of grain size and morphology. The current results are useful to set some process parameters for the ultrasonic treatment of liquid Al–Si–Mg foundry alloys prepared for semisolid processing.     

Temperature effects in aluminium melts due to cavitation induced by high power ultrasound

Abstract

Extensive research has been carried out previously in ultrasonic (cavitation) melt treatment. Such treatment can reduce grain size and improve material homogeneity. However, it is still not well understood which of the mechanisms is responsible for cavitation aided grain refinement. For better understanding of the processes which take place during solidification under the influence of ultrasonic vibrations, it is very important to consider the change in the cooling conditions during such treatment and thermal effects which are generated in the cavitation zone and in the bulk of liquid. The current paper presents the results of an experimental work on temperature effects in aluminium alloys and their impact on resultant microstructures. The results are discussed based on heat flow, nucleation and fragmentation during solidification.     

Temperature of maximal cavitation intensity of glycol ethers in ultrasonic cleaning

Ultrasonic cavitation intensity in six glycol ethers (and as reference—in tetrachloroethylene) was measured in two ultrasonic cleaners of different rated power and operating at about 40 kHz. Cavitation was measured in ca. 20 dm³ volumes of liquid at 8 different levels, every 4 mm. For each liquid the temperature of maximal cavitation intensity was looked for. It was found out that not only the cavitation intensity but also the temperature of maximal cavitation in glycol ethers depend to a high degree on the level of liquid.     

Ultrasonic fast identification of automotive body spot weld defect based on echo characteristics qualitative analysis

Abstract

Spot welds are used extensively by automobile manufacturers as an efficient method for joining sheet steel. The quality of them can be tested non-destructively by using ultrasound. But when spot weld defect happens, the current ultrasonic inspection methods of weld quality are difficult to achieve an ideal result especially for the stick weld defect which is one of the most important types of spot weld defects in the automotive body. At first, this paper detailedly analyses the echo characteristics of ultrasonic curves which can reflect different spot welding joint defects. After echo characteristics qualitative analysis of different spot weld defects, a peak value marking algorithm is developed to identify the joint defects especially the stick weld defect rapidly and efficiently through selecting and confirming many optimal characteristic parameters. Finally, a lot of experiments are performed to verify the proposed methods. The results indicate that this fast identification method is credible and the identification rate can reach 95% in total test samples.     

Measurement of residual stresses in austenitic stainless steel weld joints using ultrasonic technique

Abstract

A methodology has been developed using a non-destructive ultrasonic technique for measuring surface/subsurface residual stresses in 7 mm thick AISI type 316LN stainless steel weld joints made by activated tungsten inert gas and multipass tungsten inert gas welding processes. Measurement of residual stresses using an ultrasonic technique is based on the effect of stresses on the propagation velocity of elastic waves. Critically refracted longitudinal L _CR wave mode was employed and accurate transit time measurements were made across the weld joints. Quantitative values of the longitudinal residual stresses across the weld joints were estimated from the measured transit times and predetermined value of acoustoelastic constant for AISI type 316LN stainless steel. The nature of the residual stress profiles and their variations across the two types of weld joints were compared and interpreted.     

Capillary filling process during ultrasonically brazing of aluminium matrix composites

Abstract

Alumina borate whisker reinforced aluminium metal matrix composites were ultrasonically brazed in air. The liquid filler metal (FM) of a Zn–Al eutectic alloy could get into the clearance between composite couples by the action of ultrasonic capillarity. The velocity of the FM getting into the clearance decreases with increasing clearance width. The time exhausted to remove completely the oxide film on the surface increases with increasing clearance width. The oxide film could be removed completely and the metallurgical bonding formed under the action of ultrasonic vibration for sufficient time. The shear strength of the bond could reach up to 145 MPa (the nominal strength of the Zn–Al filler alloy).     

Influence of non-uniform ultrasonic vibration on casting fluidity of liquid aluminum alloy

The application of ultrasonic vibration to the casting process can be realized through mould (die) vibration. However, the resonant vibration of the mould is always accompanied by a non-uniform vibration distribution at different parts, which may induce a complex liquid flow and affect the casting fluidity during the mould filling process. The influence of non-uniform ultrasonic vibration on the fluidity of liquid AlSi9Cu3 alloy was studied by mould vibration with different vibration gradients. It is found that ultrasonic mould vibration can generate two opposite effects on the casting fluidity: the first, ultrasonic cavitation in melt induced by mould vibration promotes the casting fluidity; the second, the non-uniform mould vibration can induce a melt flow toward the weak vibration areas and turbulence there, consequently decreasing the casting fluidity. When the melt flow and turbulence are violent enough to offset the promoting effect of cavitation on fluidity, the ultrasonic vibration will finally induce a resultant decrease of casting fluidity. The decreasing effect is proportional to the vibration gradient.

     

基于功率超声珩磨的空化泡动力学模型的研究

功率超声珩磨是在普通珩磨的基础上施加了功率超声振动。当超声波的强度超过液体空化阈值的时候会发生空化效应,产生大量的空化泡。在对功率超声珩磨切削运动以及空化效应基本理论分析的基础上,以单个空化泡为研究对象,利用能量守恒定律,建立功率超声珩磨单个空化泡的动力学方程,为功率超声珩磨空化效应的进一步研究提供了理论支撑。     

Evolution of microstructure and phase composition of joints with ultrasonic-assisted resistance brazing

ABSTRACT

Zn–2Al alloy is used as a filler metal for brazing of aluminium 6063 alloys by ultrasonic-assisted resistance brazing (RB) technology. The evolution of the microstructure and phase composition under the effects of the electric field and ultrasonic vibration were studied. The results show that ultrasonic cavitation can remove the existing oxide films effectively and inhibit element segregation, which help obtain joints with good metallurgical bonding. In comparison to RB joints, which exhibit a coarse dendritic structure, a uniform dendritic structure was obtained in the ultrasonic-assisted resistance joints. Furthermore, the combined electric and ultrasonic field has a significant effect on grain size and on dissolution during brazing. With the application of ultrasonic vibration, the diffusion between the base metal and the Zn–2Al filler metal intensifies.     

超声作用下Ni/Sn/Ni钎焊界面金属间化合物的演变

对比研究了超声作用和无超声作用下Ni/Sn/Ni钎焊界面金属间化合物的形成和演变规律。结果表明,无超声作用时,Ni/Ni_3Sn_4界面较为平直且致密,而Sn/Ni_3Sn_4界面被液态Sn钎料逐渐溶解而呈扇贝状,并且有少量Ni_3Sn_4分布在焊缝中。其次,界面金属间化合物(intermetallic compound, IMC)层厚度与时间呈抛物线关系,Ni_3Sn_4的生长受体扩散的控制。超声作用下,声空蚀作用使得界面Ni_3Sn_4发生溶解而形成很多沟槽,甚至在界面IMC的局部区域出现了"neck"状连接,重新为母材Ni原子向钎料的溶解打开了通道,在声流的辅助作用下促进母材的溶解。随着超声时间的增加,声空化作用将界面"neck"状连接的细长的Ni_3Sn_4晶粒打碎而进入焊缝,使得界面IMC逐渐减薄。进入焊缝的Ni_3Sn_4进一步在空化作用下溶解和破碎,最终大量细小的Ni_3Sn_4均匀分布在焊缝中。     

Enhancement of AZ80 joints using ultrasonic vibration-assisted welding process

Ultrasonic vibration-assisted welding process was developed to improve the microstructures and mechanical properties of AZ80 Mg alloy joints. Results show that the ultrasonic vibration-assisted welding process has a significant effect on the morphology and size of both β-Mg₁₇Al₁₂ precipitated phases and α-Mg grains. With ultrasonic vibration treatment, the primary α-Mg grains are transformed from coarse dendrites to nearly fine equiaxed grains, and the β-Mg₁₇Al₁₂ phases at α-Mg boundaries are refined and become discontinuous, owing to the cavitation effects and acoustic streaming effects induced by ultrasonic vibration. The mechanical properties of AZ80 Mg alloy joints under the ultrasonic vibration-assisted process are obviously improved. And the influence mechanisms of the ultrasonic vibration-assisted welding process on joints are discussed in detail.     

Effect of cold flakes on mechanical properties of aluminium alloy die casts

Abstract

The cold flake was detected in aluminium alloy die casts ADC12 by using the scanning acoustic microscope, and was visualised in the acoustic image as bright and dark regions, which were corresponding to the oxide layer and the body of the cold flake respectively. By using the specimen which contains the cold flake, the tensile testing and the fatigue testing were carried out. The in process ultrasonic measurement was also carried out with a water bag in the fatigue testing to detect detachment of the cold flake from the matrix in the fatigue process. From these results, it was found that the cold flake was detached from the matrix in the fatigue process to form a crack, and cold flakes, especially exposed cold flakes, reduce the tensile strength and the fatigue life of die casts. The effect of the cold flake on the strengths was discussed from the point of crack propagation.