Microstructural Evaluation of Friction Stir Processed AZ31B-H24 Magnesium Alloy

Fairman, M.; Afrin, N.; Chen, D.L.; Cao, X.; Jahazi, Mohammad

doi:10.1179/cmq.2007.46.4.425

Cited by 25 publications

(9 citation statements)

References 13 publications

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“…where HV is Vickers hardness and D is average grain size near weld interface. Similar Hall-Petch type relationships were also reported in the FSWed AZ31-H24 Mg alloy [121,122]. It is seen that the tensile lap shear load, strength, and total failure energy first increased with increasing welding energy up to 1500 J, and then decreased with a further increase in the welding energy.…”

Section: Microhardnesssupporting

confidence: 78%

“…After welding, it can be seen from Figure 4.1(b)-(e) that the grain size became coarser, and with increasing welding energy from 500 J to 2000 J, the average grain size in the NZ increased from 7.6 to 13.6 µm. A similar increase in the grain size of NZ of AZ31-H24 Mg alloy welded joints was also observed after USW [80,82] and FSW [121,122]. The increase in the grain size was attributed to the rise in the temperature due to frictional heating and severe plastic deformation, which resulted in the partial recrystallization of elongated/deformed grains and the coarsening of original equiaxed grains in the BM.…”

Section: Microstructure Characterizationsupporting

confidence: 64%

“…It is seen that the microhardness decreased slightly with increasing energy input on the Mg side while no change occurred on the Cu side. It can be reasoned that as the heat input increased with increasing welding energy, the increase in temperature resulted in grain growth, causing a decrease in hardness based on the Hall-Petch type relationship which was observed in an AZ31B-H24 Mg alloy after friction stir welding or processing [121,122]. The unchanged microhardness on the Cu side with increasing welding energy was because the interface temperature during joining may not have reached the recrystallization temperature of Cu.…”

Section: Vickers Microhardnessmentioning

confidence: 99%

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Ultrasonic Spot Welding of Similar and Dissimilar Alloys for Automotive Applications

Macwan¹

2021

Preprint

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Lightweighting has been regarded as a key strategy in the automotive industry to improve fuel efficiency and reduce anthropogenic environment-damaging, climate-changing, and costly emissions. Magnesium (Mg) alloys and Aluminum (Al) alloys are progressively more used in the transportation industries to reduce the weight of vehicles due to their high strength-to-weight ratio. Similarly, high strength low alloy (HSLA) steel is widely used to reduce gauge thickness and still maintain the same strength, and thereby reduce vehicle weight as well. A multi-material design of automotive structures and parts inevitably involve similar Mg-to-Mg and dissimilar Mg-to-Al, Al-to-steel, and Mg-to-Cu joints. Ultrasonic spot welding (USW) – a solid-state joining technique has recently received significant attention due to its higher efficiency in comparison with conventional fusion welding techniques. In this study, USW was used to generate similar joints of low rare-earth containing ZEK100 Mg alloy sheets and dissimilar ZEK100-to-Al5754, Al6111-to-HSLA steel, and Mg-to-Cu joints at different levels of welding energy or welding time. To optimize welding process and identify key factors affecting the weld strength, microstructural evolution, microhardness test, tensile lap shear test, fatigue test, and fracture analysis were performed on similar and dissimilar ultrasonic spot welded (USWed) joints. Dynamic recrystallization and grain coarsening were observed during Mg-to-Mg similar welding while rapid formation and growth of interface diffusion layer were observed in all dissimilar joints in the present study. It was due to significantly high strain rate (~103 s-1) and high temperature generated via frictional heating during USW. The interface diffusion layer was analyzed by SEM, EDS and XRD phase identification techniques which showed the presence of eutectic structure containing intermetallic compounds (IMCs). As a result, brittleness at the interface increased. The Zn coating in dissimilar USWed Al-to-steel joints eliminated the formation of brittle IMCs of Al-F, which were replaced by relatively ductile AlZn eutectic. The optimum welding energy or welding time during similar and dissimilar USW of lightweight alloys with a sheet thickness of 1-2 mm was in the range of ~500 J to 2000 J (~0.25 s to 1 s).

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Section: Microhardnesssupporting

confidence: 78%

Section: Microstructure Characterizationsupporting

confidence: 64%

Section: Vickers Microhardnessmentioning

confidence: 99%

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Ultrasonic Spot Welding of Similar and Dissimilar Alloys for Automotive Applications

Macwan¹

2021

Preprint

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“…In comparison with the BM, the HAZ contained a greater fraction of equiaxed grains and a slightly coarser grain size due to the dominating effect of frictional heating, which resulted in the partial recrystallization of the elongated/deformed grains and the coarsening of the original equiaxed recrystallized grains in the BM microstructure in the H24 temper. This microstructural evolution observed in the different regions of the current friction stir lap welds of AZ31B-H24 Mg alloy is consistent with that appearing in the friction stir butt welds of AZ31B-H24 Mg alloy[111][112][113][114][115].The effect of the welding speed and tool rotational rate on the microstructure in the SZ is shown in Figure4.6(b)-(d) relative to the BM structure given in Figure4.6(a). It is clear that the microstructure in the SZ was significantly different from that of the BM.…”

supporting

confidence: 81%

Friction Stir Welding of AZ31B-H24 Magnesium Alloy in Lap Configuration

Naik¹

2021

Preprint

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Friction stir welding (FSW) being an enabling solid-state joining technology can be suitably applied for the assembly of lightweight magnesium alloys. In this study, AZ31B-H24 Mg alloy sheets with a thickness of 2 mm were friction stir welded in lap configuration using two tool rotational rates of 1000 and 1500 rpm and two welding speeds of 10 and 20 mm/s. The joint quality was characterized in terms of the residual stresses, welding defects, microstructure, and texture. The mechanical properties including hardness, room and elevated temperature tensile and fatigue properties were also evaluated and correlated to the structure and defects. It was observed that the hardness decreased from the base metal (BM) to the stir zone (SZ) across the heat-affected zone (HAZ) and thermomechanically-affected zone (TMAZ). The lowest value of hardness appeared in the SZ. With increasing tool rotational rate or decreasing welding speed, the average hardness in the SZ decreased owing to increasing grain sizes, and a Hall-Petch-type relationship was established. The shear tensile behavior of the lap joints was evaluated at low (-40°C), room (25°C), and elevated (180°C) temperatures. The failure load was highest in the lower heat input condition that was obtained at a tool rotational rate of 1000 rpm and a welding speed of 20 mm/s at all the test temperatures, due to a smaller hooking height, larger effective sheet thickness, and lower tensile residual stress, as compared with other two welding conditions that were obtained at a higher tool rotational rate or lower welding speed. The lap joints usually fractured on the advancing side of the top sheet near the interface between the TMAZ and the SZ. Elevated temperature testing of the weld assembled at a tool rotational rate of 1000 rpm and a welding speed of 20 mm/s led to the failure along the sheet interface in a shear fracture mode due to the high integrity of the joint that exhibited large plastic deformation and increased total energy absorption. Fatigue fracture of the lap welds always occurred at the interface between the SZ and TMAZ on the advancing side where a larger hooking defect was present (in comparison with the retreating side). The welding parameters had a significant influence on the hook height and the subsequent fatigue life. A relatively “cold” weld, conducted at a rotational rate of 1000 rpm and welding speed of 20 mm/s, gave rise to almost complete elimination of the hooking defect, thus considerably (over two orders of magnitude) improving the fatigue life. Fatigue crack propagation was basically characterized by the formation of fatigue striations concomitantly with secondary cracks.

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“…There is no significant precipitation hardening in the alloy studied (AZ31, ≃Mg-3Al-1Zn wt% wrought) and the net variation in hardness over the entire joint was within the range 45-65 HV, with the lower value corresponding to the base plate [164][165][166]. In the same system, a higher starting hardness of 70 HV leads to a substantially lower hardness in the nugget (50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60); the variations in hardness appear to be consistent with measured variations in grain size in accordance with the form of the Hall-Petch relationship [165,167]. The grains in both the nugget and TMAZ tend to be in a recrystallised form, and tend to be finer when the net heat input is smaller (for example at higher welding speeds).…”

Section: Magnesium Alloysmentioning

confidence: 99%

Recent advances in friction-stir welding – Process, weldment structure and properties

Nandan

DebRoy

Bhadeshia

2008

Progress in Materials Science

1,780

907

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Friction stir welding is a refreshing approach to the joining of metals. Although originally intended for aluminium alloys, reach of FSW has now extended to a variety of materials including steels and polymers. This review deals with the fundamental understanding of the process and its metallurgical consequences. The focus is on heat generation, heat transfer and plastic flow during welding, elements of tool design, understanding defect formation and the structure and properties of the welded materials.

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Microstructural Evaluation of Friction Stir Processed AZ31B-H24 Magnesium Alloy

Cited by 25 publications

References 13 publications

Ultrasonic Spot Welding of Similar and Dissimilar Alloys for Automotive Applications

Ultrasonic Spot Welding of Similar and Dissimilar Alloys for Automotive Applications

Friction Stir Welding of AZ31B-H24 Magnesium Alloy in Lap Configuration

Recent advances in friction-stir welding – Process, weldment structure and properties

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