Zinc Coated Steel Research Papers (original) (raw)

In order to meet the demand for lighter and more fuel efficient vehicles, a significant attempt is currently being focused toward the substitution of aluminum for steel in the car body structure. It generates vital challenge with respect to the methods of joining to be used for fabrication. However, the conventional fusion joining has its own difficulty owing to formation of the brittle intermetallic phases. In this present study AA6061-T6 of 2 mm and HIF-GA steel sheet of 1 mm thick are metal inert gas (MIG) brazed with 0.8 mm Al–5Si filler wire under three different heat inputs. The effect of the heat inputs on bead geometry, microstructure and joint properties of MIG brazed Al-steel joints were exclusively studied and characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), electron probe micro analyzer (EPMA) and high resolution transmission electron microscopy (HRTEM) assisted X-ray spectroscopy (EDS) and selective area diffraction pattern. Finally micro-structures were correlated with the performance of the joint. Diffusion induced intermetallic thickness measured by FESEM image and concentration profile agreed well with the numerically calculated one. HRTEM assisted EDS study was used to identify the large size FeAl 3 and small size Fe 2 Al 5 type intermetallic compounds at the interface. The growth of these two phases in A2 (heat input: 182 J mm −1) is attributed to the slower cooling rate with higher diffusion time (~61 s) along the interface in comparison to the same for A1 (heat input: 155 J mm −1) with faster cooling rate and shorter diffusion time (~ 24 s). The joint efficiency as high as 65% of steel base metal is achieved for A2 which is the optimized parameter in the present study.

- by and +1
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- Welding Technology, Aluminium Alloys, Welding Metallurgy, Zinc Coated Steel

Metal inert gas (MIG) brazing is a potential process
for joining coated automotive steel sheets over conventional
fusion welding process. However, understanding the process
variables on the joint performance is not yet clear. This paper
deals with details study on the effect of process parameters
and two different modes of operation (push and pull) on bead
geometry, microstructure, microhardness, nano-hardness,
shear tensile strength, and high-cycle fatigue behavior of
MIG brazed lap joint of 1.4-mm-thick zinc-coated
(galvanized) DP600 steel sheet using Cu-Al filler wire. It
has been possible to obtain 98 % joint efficiency using Cu-
Al filler wire due to dispersion hardening effect of fusion zone
consisting of dispersed iron from base metal in copper matrix.
Also, an interface region formed (∼6 μm) in-between fusion
zone and steel substrate has been characterized by X-ray and
nano-hardness testing which confirmed the presence FeAl intermetallic
compound. High-cycle fatigue test of all MIG
brazed joints showed fatigue endurance (2 million cycles) at
10 % of tensile load and fatigue life increased with increasing
heat input. Interestingly, three different fatigue failure paths
were observed with different loading cycle, such as interfacial
failure; fusion zone failure and fine grain heat-affected zone
failure where the bead geometry played an important role in
brazed joint under dynamic loading condition.

- by Dr. Sushovan Basak and +2
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- Microstructure, Welding Technology, Fatigue, Zinc Coated Steel

The gas metal arc (GMA) brazing process (a novel approach that combines GMA
welding and brazing) was applied for joining a new-generation automotive steel (interstitial-
free steel) using silicon-containing copper-based filler metal. During this joining
process, an interface region of very high hardness was developed through the
diffusion of the silicon present in the molten braze metal into the solid steel. The interface
microstructure consisted of silicon-enriched, iron-based intermediate phase
􀀀α1 for lower heat input and dispersed submicroscopic Fe5Si3 particles in 􀀀α1 matrix
for higher heat input. The calculated diffusion distance of silicon was in excellent
agreement with the measured interface width, which envisaged the diffusion of silicon
in iron matrix as the controlling factor for evolution of the interface region. The thermodynamic
calculations exhibited the lowest Gibbs free-energy change for Fe5Si3 as
compared to other compounds of Fe and Si to justify the stability of Fe5Si3 in the microstructure.
Accordingly, during tensile shear tests, the failure occurred in the base
metal region, i.e., not at the harder and stronger joint interface. These results suggested
a successful joining with 100% joint efficiency.

- by Dr. Sushovan Basak and +1
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- Microstructure, Zinc Coated Steel, If Steel, Tensile Strength

A premature corrosion failure in seam-welded galvanized steel cold water pipes was reported to occur after just 18-24 months in service. The aim of the present work was to investigate the causes of this premature corrosion of pipes, through metallographic investigations. This work comprised chemical analyses, visual examination of internal surfaces of pipes and microstructural examinations of the corrosion perforation regions (pitting corrosion areas) using optical and scanning electron microscopy with energy-dispersive x-ray analysis. The investigations showed that failures resulted from incorrect installation-pipes were installed with yellow brass ball valves. When mixed with yellow brass, galvanized steel triggers dezin-cification and results in electrolytic action when combined with nonferrous metals, such as copper and brass.

- by B. Pawłowski
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- Failure Analysis, Seam Weld Defects Assesement, Zinc Coated Steel

An indentation based method to characterize the yield locus for steel sheets is developed and implemented. Knoop hardness based indentation experiments have been performed on the surface as well as on the cross sections of an uncoated steel sheet to obtain the corresponding yield locus in the deviatoric and plane-stress situation. Stress ratios following the indenter's geometry are used to plot the yield locus from indentation data. The stress ratios have been corrected for the anisotropy of the material by an optimization algorithm. Points are then plotted in the plane-stress plane using the corrected stress ratios, the strain increment vectors and indentation hardness data. The parameters for the Hill's quadratic yield criteria are obtained from the indentation data based on a curve fitted yield locus. The results obtained using nano-indentation have been compared with those obtained from the standard characterization tests for steel sheet and shown to have good agreement. The method is also applied to the yield locus characterization of zinc coatings on steel sheet for multi-scale modelling of friction in deep drawing.

- by Tanmaya Mishra
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- Thin Films and Coatings, Anisotropy, Surface Coatings, Nano-indentation

Friction Stir welding has been attempted to study the feasibility of FSW between aluminium sheet (AA 6061) of 2 mm thick and Zinc coated steel (HIF-GA) sheet of 1 mm thick in lap joint configuration. The interfacial area of dissimilar welds has been analyzed by XRD, EPMA,TEM with EDS and nano indentation technique to identify the IMC distribution pattern depending on the combined effect of rotational speed and travel speed as well as the effect of energy and thermal cycle. The average joint strength is significantly influenced by the thermal cycle, respective torque and combined effect of rotational speed and travel speed as well as energy input. Improved joint strength between Al and coated steel could be obtained within a combination of rotational speed and travel speed as well as energy input. Force and torque response during FSW have been analyzed in terms of parameter optimization and joint performance.

- by Dr. Sushovan Basak and +1
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- Microstructure, Friction Stir Welding, Zinc Coated Steel

Friction stir welding has been attempted to evaluate joint strength of lap joint between aluminum sheet (AA6063) and zinc-coated steel (HIF-GA) sheet under different combination of rotational speed and traverse speed. The shear strength decreases significantly when rotational speed increases from 700 to 1,500 rpm at a traverse speed of 30 mm/min. At traverse speed of 50 mm/min, increasing rotational speed from 700 to 1,500 rpm, shear strength remains more or less the same. However, at a traverse speed of 100 mm/min, the shear strength increases significantly with increasing rotational speed from 700 to 1,500 rpm. Essentially, higher fracture load of the lap joint is obtained within a certain range of energy. The results have been correlated with the microstructural characteristics at the bond interface using energy dispersive X-ray spectroscopy, electron probe micro analyzer, and X-ray diffraction. The results show that characteristics of intermetallic compound formed at the interface derived from energy input takes predominating role towards lap joint of Al and coated steel. Furthermore, force and torque responses influenced by the processing parameters can be utilized as weld quality check.

- by Dr. Sushovan Basak and +1
- •
- Microstructure, Friction Stir Welding, Intermetallic Compounds, Zinc Coated Steel