Microstructure Of Weld Zone Research Articles

Investigation on Mechanical Properties and Microstructure of SSM 356-T6 Aluminium Alloy by Diffusion Bonding

SSM 356-T6 aluminium alloys generally present low weldability by fusion methods because of the sensitivity to weld solidification cracking, porosities, change microstructure in weld zone and other defects in the fusion zone. Diffusion bonding can be deployed successfully with aluminium alloys. This paper presents the technique to conserve the globular weld structure of SSM 356-T6 aluminium alloy. The effect of joining parameters on the microstructure and mechanical properties of diffusion bonding butt joints of semi-solid metal 356-T6 aluminium alloy were investigated by conditions as follows: contact pressure at 0.4, 0.9, 1.8, 2.4 and 2.7 MPa, for 3 hours holding time and temperature at 495°C under argon atmosphere at 4 liters per minute. The results showed that condition used contact pressure 2.4 MPa, with 3 hours holding time and temperature at 495°C, under argon atmosphere provided. The highest joint strength reaching to 182.2 MPa, which had joint efficiency of 61.34 percents compared with base material. In addition, microstructure in welded zone after welding is still in globular structure, but the grain size was increased when the higher bonding temperature was used. The results of this investigation have shown that an average hardness is around 121.2 HV.

Effect of process parameters on tensile strength of friction stir welded cast A356 aluminium alloy joints

A356 is a high strength aluminium-silicon cast alloy used in food, chemical, marine, electrical and automotive industries. Fusion welding of this cast alloy will lead to many problems such as porosity, micro-fissuring, and hot cracking. However, friction stir welding (FSW) can be used to weld this cast alloy without above mentioned defects. An attempt was made to study the effect of FSW process parameters on the tensile strength of cast A356 aluminium alloy. Joints were made using different combinations of tool rotation speed, welding speed and axial force. The quality of weld zone was analyzed by macrostructure and microstructure analyses. Tensile strengths of the joints were evaluated and correlated with the weld zone hardness and microstructure. The joint fabricated using a rotational speed of 1000 r/min, a welding speed of 75 mm/min and an axial force of 5 kN showed a higher tensile strength compared to the other joints.

A simple analytical model for estimation of melt film variables in thermoplastic vibration welding

The strength of vibration welds of thermoplastics is governed by the weld zone microstructure, which in turn, is closely tied to the welding process variables, such as the thickness of the weld melt film and the temperature profiles therein. The mathematical model described in this report is aimed at describing the role of the rheology of the melt—specifically the magnitude and shear rate dependence of the melt viscosity—in governing the melt film variables during the steady state penetration phase (Phase III) of vibration welding. The steady state momentum balance and heat transfer within the melt film are solved by using the power law model for viscosity. Closed-form analytical expressions are obtained for estimating the melt film thickness, the shear rates, and the temperature field within the film. This model has been used to estimate weld zone variables for four different polymers displaying a wide range of viscosities and shear thinning behaviors. POLYM. ENG. SCI., 54:499–511, 2014. © 2013 Society of Plastics Engineers

Microstructure and defect of titanium alloy electron beam deep penetration welded joint

The microstructure, phase composition and cold shut defect of thick titanium alloy electron beam welded joint were studied. The results showed that the microstructure of weld zone was composed of α′ phase; the heat affected zone was divided into fine-grained zone and coarse-grained zone, the microstructure of fine-grained zone was primary α phase + β phase + equiaxed α phase, and the microstructure of coarse-grained zone was primary α phase + acicular α′ phase; the microstructure of base metal zone basically consisted of primary α phase, and a small amount of residual β phase sprinkled. The forming reason of cold shut was analyzed, and the precaution of cold shut was proposed.

A comparative study of the microstructure and mechanical properties of HTLA steel welds obtained by the tungsten arc welding and resistance spot welding

Hardness tests are routinely employed as simple and efficient methods to investigate the microstructure and mechanical properties of steels. Each microstructural phase in steel has its own hardness level. Therefore, using surface hardness mapping data over a large area of weld zone would be a reasonable method to identify the present phases in steel. The microstructure distribution and mechanical properties variation through welded structures is inhomogeneous and not suitable for certain applications. So, studying the microstructure of weld zone has a significant importance. 4130 steel is classified in HTLA steels and it is widely used in marine industry due to its superior hardenability, good corrosion resistance and high strength. Gas tungsten arc and resistance spot welding are the most usable processes in joining of 4130 sheets. In this work a series of welds have been fabricated in 4130 steel tube by gas tungsten arc and resistance spot welding. The tube was subjected to quench-tempered heat treatment. Slices from the welds before and after heat treatment were polished and etched and the macrostructure and microstructure were observed. Hardness maps were then determined over the large area of weld zone, including the heat affected zone and base plate. Results show good relations between the various microstructures, strength and hardness values. It is also proved that this method is precise and applicable to estimate phase fraction of each phase in various regions of weld. In the current study some equations were proposed to calculate the ultimate tensile stress and yield stress from the weld. The calculated data were compared with experimental data obtained by tensile test. Average relative error between data prepared by these two methods has a very acceptable value around 5%.

Effects of laser beam welding parameters on mechanical properties and microstructure of AZ31B magnesium alloy

The effects of laser beam welding process parameters such as laser power, welding speed and focal position on mechanical properties and microstructure of AZ31B magnesium alloy were studied. Nine joints were fabricated using different levels of laser power, welding speed and focal position. Tensile properties of the welded joints were evaluated and correlated with the weld zone microstructure and hardness. It is found that the joints fabricated using a laser power of 2 500 W, welding speed of 5.5 m/min and focal position of −1.5 mm yield superior tensile properties compared with the other joints. The formation of very fine grains in weld region, higher fusion zone hardness and uniformly distributed finer precipitates are the main reasons for superior tensile properties of these joints.

Research on the Forming Mechanism of Micro-Moulds Based on Laminated Slip-Welding of Ultrathin Stainless Steel Foils

To address the mainstream technology of UV-LIGA combined with micro-electroforming which could only fabricate micro-moulds cavity with vertical wall structure and low depth-to-width ratio, a new forming process based on femtosecond laser combined with laminated slip-welding was proposed in the paper. The forming process was achieved through experiment and it proved that the forming process could be a useful method for the process of micro-moulds with high depth-to-width ratio and complex structures. Work-pieces which were 0Cr18Ni9 stainless steel foils whose thickness was 20μm were welded by resistance welding machine and the microstructure of welding-zone was observed in detail. It was found that the welding-zone was composed of nugget zone, fusion zone and heat affected zone. Through the study of welding mechanism, the cooling rate of nugget zone was 3.99×104K/s and there was dynamic recrystallization in nugget zone. For further study, through the X-ray diffraction (XRD) test, it was found there were no chromium carbide and iron-copper eutectic alloy in nugget zone.

Investigation of the effects of critical process parameters of friction stir welding of polyethylene

Friction stir welding is a solid-state method of joining thermoplastic materials. This paper studied the effect that varying process parameters (rotational speed, welding speed, and attack angle) had on the weld quality of polyethylene sheets. Experiments were performed at rotational speeds of 1000, 1200, 1400, 1600, and 1800 r/min, welding speeds of 12, 16, and 20 mm/min, and attack angles of 1° and 2°. A strength value of 75 per cent of that of the base material was achieved at the isolated optimum welding condition. Changes in the weld zone microstructure were investigated using differential scanning calorimetry and scanning electron microscopy. The observed microstructures were used to explain the reduced value of the strength.

Microstructure simulation and ballistic behaviour of weld zones in friction stir welds in high strength aluminium 7xxx plate

The effect of friction stir welding (FSW) on the knockdown in properties and failure mechanisms of high strength aluminium plate (AA7010-T7651) under ballistic impact has been investigated by modelling and ballistic testing, simulated, and actual weld zone microstructures, in order to systematically study the link to weld microstructural variation. FSW of thick plate leads to an extremely wide heat affected zone (HAZ). The microstructures within the weld zones were successfully modelled and simulated. However, the maximum loss of hardness in the HAZ resulted in only a 20% reduction in the ballistic limit (V50). The maximum V50 was associated with the highest level of hardness reached prior to a change in failure mechanism, from ductile hole enlargement, using an armour piercing (AP) projectile, or plugging with a fragment simulation projectile (FSP) to excessive spalling and associated adiabatic shear banding at too high hardness levels. The behaviour of the nugget zone has also been examined. The trends in the ballistic data are discussed in the context of the weld zone microstructures and fracture mechanisms.

An experimental investigation on friction stir welding of AZ31B magnesium alloy

The conventional fusion welding of magnesium alloys often produces porosity in the weld joint, which deteriorates its mechanical properties. To solve this problem, friction stir welding (FSW), a solid-state welding technique, can be applied for joining of magnesium alloys. In this investigation, an attempt was made to understand the effect of FSW process parameters such as tool rotational speed, welding speed, and axial force on tensile properties of AZ31B magnesium alloy. Fourteen joints were fabricated using different levels of tool rotational speed, welding speed, and axial force. Tensile properties of the welded joints were evaluated and correlated with the weld zone microstructure and hardness. From this investigation, it is found that the joints fabricated using a tool rotational speed of 1,600 rpm, a welding speed of 0.67 mm/s, and an axial force of 3 kN yielded superior tensile properties compared to other joints. Optimum level of heat generation, formation of finer grains, and higher hardness are the main reasons for the superior tensile properties of these joints. Fatigue properties of FSW joints were evaluated, and it was found that fatigue properties of FSW joints were slightly lower than the base metal.

Optimisation of friction stir welding process parameters to weld cast aluminium alloy A413 – an experimental approach

A413 is a high strength eutectic aluminium silicon cast alloy used in the food, chemical, marine, electrical and automotive industries. Fusion welding of these cast alloys can lead to problems such as porosity, microfissuring and hot cracking, etc. However, friction stir welding can be used to weld these cast alloys effectively, without defects. In this investigation, an attempt was made to optimise the friction stir welding process parameters for joining the cast aluminium alloy A413. Joints were made using four levels each of tool rotation speed, welding speed and axial force. The quality of the weld zone was analysed using macrostructure and microstructure analysis. Tensile strength of the joints were evaluated and correlated with the weld zone hardness and microstructure. The joint fabricated using a tool rotation speed of 900 rev min−1, a welding speed of 75 mm min−1 and an axial force of 3 kN showed the best tensile strength.

Influences of process parameters on tensile strength of friction stir welded cast A319 aluminium alloy joints

Fusion welding of cast A319 (Al-Si-Cu) alloy will lead to many problems including porosity, micro-fissuring, and hot cracking. Friction Stir Welding (FSW) can be used to weld A319 alloy without these defects. In this investigation, an attempt has been made to study the effect of FSW process parameters on the tensile strength of A319 alloy welded joints. Joints were made using different combinations of tool rotation speed, welding speed, and axial force, each at four levels. The quality of weld zone was analyzed using macrostructure and microstructure analysis. Tensile strength of the joints were evaluated and correlated with the weld zone microstructure. The joint fabricated with a 1200 rpm tool rotation speed, 40 mm/min welding speed, and 4 kN axial force showed superior tensile strength compared with the other joints.

Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy – An experimental approach

In this investigation, an attempt was made to select proper tool pin profile, tool shoulder diameter and tool material to friction stir weld AZ31B magnesium alloy. Five tool pin profiles, five tool materials and three tool shoulder diameters were used to fabricate the joints. Tensile properties of the joints were evaluated and correlated with the weld zone microstructure and hardness. From this investigation, it is found that the joint fabricated using threaded pin profiled tool made of high carbon steel with 18 mm shoulder diameter produced mechanically sound and metallurgically defect free welds compared to their counterparts. The absence of defects in weld region, presence of very fine equiaxed grains in the weld region and higher hardness in the weld region are the main reasons for superior tensile properties of these joints.

Microstructure and high strength–toughness combination of a new 700 MPa Nb-microalloyed pipeline steel

A new ultrahigh strength niobium-microalloyed pipeline steel of yield strength ∼700 MPa has been processed. The Charpy impact toughness at 0 °C was 27 J and tensile elongation was 16%. The ultrahigh strength is derived from the cumulative combination of fine grain size, solid solution strengthening with additional interstitial hardening, precipitation hardening from carbides, dislocation hardening, and mixed microstructure. The microstructure was characterized by polygonal ferrite, upper bainite, degenerated pearlite, and martensite–austenite (MA) constituents. The microstructure of weld and heat-affected zone (HAZ) was similar to the base metal such that the hardness is retained in the weld region implying insignificant softening in the weld zone. Niobium and titanium precipitates of different morphology and size range evolved during thermomechanical processing and include rectangular (∼500 nm), irregular (∼240–500 nm), cuboidal/spherical (∼125–300 nm), and very fine (<10 nm). They were generally MC type of carbides. An important aspect of the developed steel is significantly lean chemistry.

Characterization of complex, solid-state flow and mixing in the friction-stir welding (FSW) of aluminum alloy 6061-T6 to magnesium alloy AZ91D using color metallography

Semi-solid-cast magnesium (Mg) alloy AZ91D (3% solid fraction) was friction-stir welded (FSW) to aluminum (Al) alloy 6061-T6 in continuous non-porous welds. The resulting welds were analyzed in order to understand the solid-state mixing mechanisms that create the chaotic intercalated weld zone microstructure characterized by swirls and vortexes of dynamically recrystallized material. Severe plastic deformation in the solid-state is accommodated by the dynamic recrystallization of the mechanically mixed materials which generates a fine-grained weld zone microstructure, along with dislocation substructures and precipitates. Mg–Al weld systems are also characterized by eutectic/intermetallic regimes that are thrice as strong as the base materials, and nearly six times stronger than some of the softer recrystallized regimes abutting them. Color metallography was used to gain additional information about the varying regimes within the intercalated microstructure. The variation in coloration indicated energy differences between the various dynamically recrystallized microstructural regimes, in turn providing correlations between the general coloration of these regimes, and their nature and strength. The weld zone is strengthened by the coexistence of the hard eutectic/intermetallic weld regimes with the abutting softer dynamically recrystallized regimes across a continuous interface.

Structure, properties and fracture of friction stir welds in a high-temperature Al-8.5Fe-1.3V–1.7Si alloy (AA-8009)

Friction stir welds produced in a rapidly-solidified, powder metallurgy Al-8.5Fe-1.3 V-1.7 Si (wt.%) alloy were characterized in order to investigate the effects of deformation during welding on the weld zone microstructure, hardness, tensile properties, and fracture behavior. A weld produced using a tool rotational speed of 1200 rpm and a traversing rate of 4.3 mm/s exhibited a repetitive pattern of dispersoid-depleted bands that were attributed to the intense deformation that occurred in the vicinity of the tool. The significant softening associated with these regions, and the presence of occasional, irregularly-shaped voids near the boundary between the base metal and the weld zone on the advancing side of the weld, promoted a weld tensile strength of 60–70% of the base metal. The application of a lower tool rotational speed of 428 rpm and a lower traversing rate of 1.9 mm/s promoted fewer bands and a more uniform dispersoid distribution throughout the weld zone, and an absence of defects along the weld zone/base metal interface. Tensile strength of these welds approached 90% of the base metal. Fracture of the transverse-weld oriented tensile specimens for both weld types consistently occurred near the boundary between the weld zone and the base metal on the advancing side of the weld zone, with tensile specimen ductilities appreciably lower than that of the base metal.

Microtexture Analysis of Friction Stir Welded Al 6061-T651 Plates

Microstructural characteristics of friction-stir-welded Al 6061-T651 with varying rotating and advancing speed were examined by the electron backscattering diffraction (EBSD) installed in field emission-scanning electron microscopy (FE-SEM). It was found that FSW produced an equiaxed fine-grained microstructure in weld zone and the grain size in weld zone decreased up to about 4~6 µm with decreasing rotating speed. The primary textures developed in weld zone were {100}&lt;001&gt;, {110}&lt;001&gt; and {111}&lt;110&gt;. In thermo-mechanical affected zone, the change in grain size was not significant, however, large number of low angle grain boundaries were observed, which seems to be concerned with the formation of subgrains due to the development of dislocation cells.

Microstructure and residual stress variations in weld zone of flash-butt welded railroads

In the weld zone and base metal contiguous to the weld zone in flash-butt welded rail, the web of the rail has high tensile residual stresses and the head and base of the rail have compressive residual stresses. The web region is susceptible to failure since most of the weld zone of the rail is coarse grained and has porosity, inclusions and defects resulting from rapid solidification of molten metal entrapment in the weld. Efforts to reduce the amount of these tensile residual stresses require recognition of their causes. In this research, microscopic and macroscopic studies were carried out on vertical and horizontal sections of the weld zone in the head, web and base of the rail. Just after flash-butt welding, the temperature of the web between the current carrying copper electrodes is higher than the temperature of the head and base of the rail. Therefore, by cooling the weld zone to room temperature, the amount of web contraction between the electrodes is higher than the amount of base and head contraction and consequently tensile residual stresses are produced in the web at and near the weld zone. In the head and base of the rail, compressive residual stresses are developed.

Friction-stir welding of a beryllium-aluminum powder metallurgy alloy

The friction-stir welding of a 62 Be-38 Al composite consisting of a Be phase in a continuous Al matrix produced a recrystallized, refined weld zone microstructure with intermixed, equiaxed grains of Be and Al, which increased in hardness by 43 percent from the base metal hardness. Like other friction-stir weld processes, there was no melting and no apparent release of airborne Be or BeO, rendering the process environmentally and technically attractive.