شکست خستگی در اتصال جوش داده شده آلیاژ آلومینیوم

Features of AcousticEmission Signals during the Initiation 

of a Fatigue Failure in a Welded Joint of an Aluminum Alloy

of the Al–Cu–Mn System

ویژگی های سیگنال انتشار آکوستیک در طول شروع یک شکست خستگی

در یک اتصال جوش داده شده آلیاژ آلومینیوم سیستم Al-Cu-Mn

ABSTRACT

The features of the generation of acoustic emissions (AEs) during the initiation of a fatigue failure in various zones of a welded joint of thermally hardened 2219T6grade aluminum alloy, which is produced using electronbeam welding, are  considered. Metallographic studies showed that a welded joint of the alloy is structurally and mechanically inhomogeneous. This predominantly influ ences the initiation and development kinetics of fatigue cracks in the joint and the AE kinetics. It is shown that the area of a formed flaw is proportional to the sum of the amplitude of detected signals, and the transition from the initiation to the stable propagation of a failure is accompanied by an abrupt increase in AE activity.

 

جوشکاری فولاد زنگ نزن 316 به روش تیگ TIG-welded 316 stainless steel

Acoustic emisson and ultrasonic wave characteristics

in TIG-welded 316 stainless steel

مشخصات انتشار آکوستیک و امواج مافوق صوت در

فولاد ضد زنگ 316 جوش داده شده به روش TIG

ABSTRACT

A TIG welded 316 stainless steel materials will have a large impact on the design and the maintenance of invessel components including pipes used in a nuclear power plant, and it is important to clear the dynamic behavior in the weld part of stainless steel. Therefore, nondestructive techniques of acoustic emission (AE) and ultrasonic wave were applied to investigate the damage behavior of welded stainless steel. The velocity and attenuation ratio of the ultrasonic wave at each zone were measured, and a 10 MHz sensor was used. We investigated the relationship between dynamic behavior and AE parameters analysis and derived the optimum parameters to evaluate the damage degree of the specimen. By measuring the velocity and the attenuation of an ultrasonic wave propagating each zone of the welded stainless steel, the relation of the ultrasonic wave and metal structure at the base metal, heat affected zone (HAZ) metal and weld metal is also discussed. The generating tendency of cumulated counts is similar to that of the load curve. The attenuation ratios from the ultrasonic test results were 0.2 dB/mm at the base zone, and 0.52 dB/mm and 0.61 dB/mm at the HAZ zone and weld zone, respectively.

 

محدوده دمایی برای تشکیل منطقه GP در آلیاژ آلومینیوم-منیزیم-روی

The Temperature Limit for GP Zone Formation

in an Al-Zn-Mg Alloy

محدوده دمایی برای تشکیل منطقه GP در آلیاژ آلومینیوم-منیزیم-روی  

ABSTRACT

The temperature limit for GP zone formation, Tlimit was determined for an Al-5 pct Zn-2 pct Mg alloy by examining the formation process of the intermediate phase. Studies of changes in hardness and electrical resistivity, together with electron metallography permitted a conclusion that the Tlimit for this alloy is 125 °C. The nucleation mechanism of the intermediate phase is also discussed. Two types of precipitation mode were found the partly coherent phase;i.e. heterogeneous nucleation on GP zones and homogeneous nucleation respectively. It is concluded that the dominant nucleation mode is determined by the quenching conditions.

 

مناطق GP در آلیاژهای Al-Zn-Mg و نقش آنها در پیرسازی مصنوعی

GP-zones in Al–Zn–Mg alloys and their role in artificial aging

مناطق GP در آلیاژهای Al-Zn-Mg و نقش آنها در پیرسازی مصنوعی

ABSTRACT

The structure of GP-zones in an industrial, 7xxx-series Al–Zn–Mg alloy has been investigated by transmission electron microscopy methods: selected area diffraction, conventional and high-resolution imaging. Two types of GP-zones, GP(I) and (II) are characterized by their electron diffraction patterns. GP(I)-zones are formed over a wide temperature range, from room temperature to 140–150°C, independently of quenching temperature. The GP(I)-zones are coherent with the aluminum matrix, with internal ordering of Zn and Al/Mg on the matrix lattice, suggested to be based on AuCu(I)-type sub-unit, and anti-phase boundaries. GP(II) are formed after quenching from temperatures above 450°C, by aging at temperatures above 70°C. The GP(II)-zones are described as zinc-rich layers on {111}-planes, with internal order in the form of elongated <110> domains. The structural relation to the η′-precipitate is discussed.

 

طیف مادون قرمز منیزیم و آلومینیم ‎جایگزین فریت‎های لیتیوم

Far-infrared spectral studies of magnesium and aluminum

co-substituted lithium ferrites

بررسی‎های طیف مادون قرمز دور منیزیم و آلومینیم جایگزین فریت‎های لیتیوم 

ABSTRACT

Polycrystalline MgxAl2xLi0.5(1−x)Fe2.5(1−x) O4 (x = 0.0, 0.2, 0.5, 0.6 and 0.7) ferrites were prepared by standard ceramic method, and characterized by X-ray diffraction and infrared absorption spectroscopy. The spectra show two significant absorption bands in the wave number range of 400–1000 cm−1 arising from interatomic vibrations in the tetrahedral and octahedral coordination compounds. The decrease in intensity and increase in broadness of bands with concentration (x) are explained on the basis of cation distribution. The force constants and bulk modulus are found to decrease with Mg-Al content (x) which suggested weakening of interatomic bonding. An alternate method for the determination of bulk modulus, longitudinal and transverse velocities is suggested. The magnetic and electrical properties of these compounds are explained in the light of structural and optical properties.

 

توزیع یونی و مغناطیسی کردن آلومینیوم جانشین فریت های لیتیمی

Ion distribution and saturation magnetization of

aluminum substituted lithium ferrites

توزیع یونی و مغناطیسی کردن آلومینیوم جانشین فریت های لیتیمی 

ABSTRACT

Ion distribution is determined in a series of aluminum substituted lithium ferrites by carefully analyzing the powder X-ray diffraction patterns. A new finding is that Al+3's substitute the Fe+3's in tetrahedral sites as well as in octahedral sites of the spinel structure. The proper formula, then, is (Fe1-a+3Ala+3)[Li0.5 +Fe1.5-(x-a)Alx-a+3]O 4, where a is approximately 0.23x2+0.22x. The saturation magnetizations are calculated and compared with the measured values.

 

مکانیزم نفوذ فلاکس در جوشکاری تیگ برای آلیاژ آلومینیوم

Study of mechanism of activating flux increasing

weld penetration of AC A-TIG welding for aluminum alloy

مطالعه مکانیزم افزایش مکانیزم نفوذ فلاکس فعال ساز جوشکاری AC  A-TIG

برای آلیاژ آلومینیوم

ABSTRACT

When multi-component flux AF305 is used as surface activating flux for an aluminum alloy, the weld penetration of activating flux-tungsten inert-gas (A-TIG) welding is over two times more than that of conventional TIG welding. Using A-TIG welding with the modes of alternating current (AC), direct current electrode negative (DCEN) and direct current electrode positive (DCEP), respectively, the flux differently affects weld penetration when the polarity is different. After studied the effect of compelled arc constriction on weld penetration of AC welding, it is believed that the constriction of the whole arc root is not the main mechanism that flux AF305 dramatically improves weld penetration. The penetration has a relationship with the separate distribution of slag on the weld surface. Then, an observation of scanning electron microscopy (SEM) and an electronic data systems (EDS) analysis of slag were performed respectively. The separate distribution of slag on the weld pool during welding and the great constriction of arc spots were confirmed by TIG welding with helium shielding gas. The relationship between slag distribution and weld penetration was studied by adding aluminum powder into flux AF305 to change the distribution of slag. During welding, the separate distribution of slag on the weld pool results in the great constriction of arc spots, an increase in arc spot force, and an increase in Lorentz force within the arc and weld pool. Finally, the weld penetration is increased.

 

جوشکاری تیگ آلومینیوم و منیزیم

اتصال آلومینیوم و منیزیم از طریق جوشکاریA-TIG

 با پیش نورد کمکی همراه با لایه میانی روی 

ABSTRACT

AZ31B Mg and 6061 Al alloys were successfully welded via a novel pre-roll-assisted A-TIG welding technique with Zn interlayer at an overlap configuration. The rolling operation increased the contact area and control tightly between Zn interlayer and plates at an interlayer-assisted overlap configuration to avoid the adverse effect of gaps. B2O3 activating flux was coated on the upper Al plates to provide contraction of the arc column to increase the arc energy density; welding penetration was increased without improving heat input, which reduced the formation and grain coarsening of Al–Mg IMCs. Therefore, the tensile–shear strength of the joints was improved obviously. The average of tensile–shear strength joined was 71.2 MPa with a maximum of 74 MPa compared to 41.1 MPa with a maximum of 45.2 MPa by conventional TIG with Zn interlayer.

 

انتقال بین مرزدانه با زاویه کم و زیاد

Transition between low and high angle grain boundaries 

انتقال بین مرزدانه با زاویه کم و زیاد 

ABSTRACT

The migration of planar, symmetric tilt grain boundaries with different tilt axes was investigated. The driving force for the grain boundary migration was due to an external mechanical stress field. Low as well as high angle grain boundaries can move under this driving force and the activation parameters for the stress induced grain boundary motion are different for low and high angle grain boundaries. The experiments showed a sharp transition from low angle grain boundary to high angle grain boundary behavior. The transition is marked by a clear change in the activation enthalpy for the grain boundary motion without any extended range. We present an overview of the existing experimental results and theoretical considerations of the structure of grain boundaries at the transition. The observation that the transition depends on the rotation axis of the grain boundary and on the grain boundary plane is particularly important, because this will influence the Brandon criterion which is often used in experiments and simulations of grain growth and recrystallization processes. 

 

ساختار مرزدانه‌های زاویه - باز The structure of high-angle grain boundaries

The structure of high-angle grain boundaries

ساختار مرزدانه‌های زاویه - باز

ABSTRACT

A coincidence model of high-angle grain boundaries can be extended to include deviations from coincidence. The generalised boundary has a terraced structure, corresponding to the densely packed planes in the coincidence lattice, and a superimposed dislocation network, corresponding to a sub-boundary in the coincidence lattice. This model is a natural extension of previous dislocation models and models based on coincidence relationships. The model explains many of the observed properties of grain boundaries and should have wide validity for the cubic system.