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Book ChapterDOI

Investigation of Process Parameters for Friction Stir Processing (FSP) of Ti-6Al-4V Alloy

TL;DR: In this paper, the effect of tool traverse speed and tool rotation speed on microstructure evolution in the stir zone (SZ) of the Ti-6Al-4V alloy was carried out.
Abstract: In the current work friction stir processing of the Ti-6Al-4V alloy was carried out. Various process parameters (tool traverse speed and tool rotation speed) were studied for successful FSP of Ti-6Al-4V. The process parameters were identified using macrostructure observation on the surface of processed plate and microstructure evolution in the stir zone (SZ) of the FSP specimen. The effect of tool traverse speed and tool rotation speed on microstructure evolution in the SZ, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) were studied. The microstructure transformation from initial elongated α structure to prior β grains, with α layer grain boundary consisting of mixture of acicular α′ and very fine lamellar α/β colonies, was observed at SZ. This was the case for wide range of variations in parameters except for the tool rotation speed of 600 rpm and traverse speed of 60 and 100 mm/min. Under this combination of parameters, the bands of DRX α and transformed β structure were observed to evolve at SZ.
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Journal ArticleDOI
TL;DR: In this paper, the authors proposed terminology to standardize the descriptions of the microstructures created during FSP and FSW of titanium alloys, and also described the microstructure changes that occur in the stir zone (SZ), transition zone (TZ), and heat-affected zone (HAZ) during friction stir welding of Ti-6Al-4V.
Abstract: Friction stir processing (FSP) was used to modify the coarse fully lamellar microstructure on the surface of investment-cast and hot isostatically pressed (HIP) Ti-6Al-4V plate. The α colony and platelet structure in the base material (BM) was refined such that the effective slip length was reduced from the α colony size of the BM, several hundred microns, to that of fine equiaxed primary α grains that are on the order of 1 μm. This change in the microstructure resulting from FSP is expected to increase fatigue crack initiation resistance making it beneficial for titanium components for aerospace applications. The as-cast coarse lamellar microstructure has superior fatigue crack growth resistance compared to other microstructures that can be obtained by thermomechanical processing. Thus, it is likely that an increase in fatigue life is obtainable by FSP. Given the growing interest in friction stir welding (FSW) and FSP of titanium alloys, we believe some consistent microstructural descriptors will help avoid confusion. Accordingly, we propose terminology to standardize the descriptions of the microstructures created during FSP and FSW of titanium alloys. We also describe the microstructure changes that occur in the stir zone (SZ), transition zone (TZ), and heat-affected zone (HAZ) during FSP of Ti-6Al-4V.

72 citations

Journal ArticleDOI
TL;DR: In this paper, a defect-free friction stir processed (FSP'd) materials were evaluated by tensile tests on 2mm-thick Ti-6Al-4V sheets using various processing parameters including tool rotational speed (800-1000 RPM) and tool traverse speed (1 4 ).
Abstract: Friction stir processing (FSP) trials were performed on 2 mm-thick Ti–6Al–4V sheets using various processing parameters including tool rotational speed (800–1000 RPM) and tool traverse speed (1–4 IPM). A processing window was established with the W–1% La 2 O 3 tool to produce defect-free friction stir processed (FSP'd) materials. The stir zone (SZ) material of the FSP'd samples showed a fully β transformed microstructure characterized by typical basket-weave lamellar α/β structure. The prior β grains in the SZs contained multiple α variants, and the average sizes ranged from 12 μm to 38 μm influenced by the processing parameters. Based on metallurgical evaluation, the microstructural evolution in different regions from base material (BM) through heat-affected zone (HAZ) and thermomechanically affected zone (TMAZ) to SZ was established. The mechanical properties of the SZs were evaluated by tensile tests. Compared to the base material, the processed samples exhibit higher tensile strength and comparable ductility. The tensile strength was affected by the microstructure of the prior β grain size and α colony size, which are controlled by processing parameters. The lower tool rotational rate and/or higher traverse speed produced a lower peak temperature and a shorter dwell time above the β-transus temperature in the SZ, which resulted in finer prior β grains and smaller α colonies, leading to higher tensile strength.

72 citations

Journal ArticleDOI
TL;DR: Friction stir welding of titanium alloy (Ti-6Al-4V) was demonstrated on 3, 6, 9 and 12 mm thickness square groove butt joints as mentioned in this paper, and complete microstructural and microhardness evaluations were conducted in addition to surface and subsurface examinations.
Abstract: Friction stir welding of titanium alloy (Ti–6Al–4V) was demonstrated on 3, 6, 9 and 12 mm thickness square groove butt joints. Complete microstructural and microhardness evaluations were conducted in addition to surface and subsurface examinations for each case. The 3 mm welds exhibited an extremely fine grained microstructure with evidence of processing temperatures below the beta transus temperature of the alloy. The 6, 9 and 12 mm samples possessed larger grains formed by a slower cooling rate from above the beta transus temperatures. The thick section weld exhibited a nearly uniform microhardness, while the thinner welds showed a slight, 6%, increase in hardness compared with the parent material.

71 citations

Journal ArticleDOI
TL;DR: In this paper, the peak temperatures during friction stir welding of Ti-6Al-4V alloy were determined as a function of the processing conditions such as tool rotation speed and feed rate.
Abstract: Experimental measurements were made to determine the peak temperatures during friction stir welding of Ti–6Al–4V alloy as a function of the processing conditions such as tool rotation speed and feedrate It was found that the spindle speed has a dominant effect on peak temperatures, while feedrate controls exposure time Low spindle speed conditions lead to peak temperatures near, or below, the beta transus temperature of the material, 1000°C (1800°F), while high spindle speed welds result in peak temperatures above 1200°C (2100°F) Weld microstructures were also evaluated as a function of the weld parameters Higher spindle speeds and lower federate lead to increased grain size

61 citations

Journal ArticleDOI
TL;DR: In this paper, the UFG microstructure of Al-30Si alloy formed by friction stir processing (FSP) was correlated with its corrosion property. And the correlation of grain and silicon particle size on corrosion properties reveals Hall-Petch type relationship.

55 citations