Technical ReportEstablishing relationship between the base metal properties and friction stir welding process parameters of cast aluminium alloys
Introduction
The usage of cast aluminium alloys in automotive and aerospace applications is ever increasing due to their light weight and castability. It is necessary to weld aluminium castings to themselves or to wrought alloys for various applications. These alloys are not easily weldable by conventional fusion welding techniques because the quality of the welded joint is deteriorated due to the presence of porosity, hot cracking and distortion. Friction stir welding (FSW) process is an emerging solid state joining process in which the material that is being welded, does not melt and recast [1]. FSW creates the weld joint without bulk melting. In addition, the extensive thermomechanical deformation induces dynamic recrystallization and recovery that refine the microstructure of the stir region. Therefore, welds made by FSW are shown to have much improved mechanical properties than the corresponding fusion welds. Since, FSW is a solid state process and the material under the rotating action of non-consumable tool has to be stirred properly to get good, defect free welds [2]. The material flow behaviour is predominantly influenced by the material properties such as yield strength, ductility and hardness of the base metal, tool design [3] and FSW process parameters.
There have been lot of efforts to understand the effect of process parameters on material flow behaviour, microstructure formation and mechanical properties of friction stir welded joints. Cavaliere et al. [4] studied the effect of welding parameters on mechanical properties of AA6056 and found that tensile strength and ductility of the joints are mainly influenced by rotation speed and welding speed. Ma et al. [5] studied the effect of friction stir processing (FSP) on microstructure of cast A356 aluminium alloy and found that FSP parameters had a significant effect on the macrostructure of the stirred zone. The welding speed had a significant effect on the tensile properties and fracture locations of the joints FSW joints [6]. In FSW joints of ADC12 aluminum die casting alloy it is found that the average diameters of the Si particles decrease with the increasing welding speed from 250 to 750 mm/min in all the regions. It is considered that the welding speed influences the heat input during the FSW, and the heat input affects the size of the Si particles [7]. The axial force on the tool decides the weld formation of FSW of aluminium alloy [8]. Most of the researchers focused on finding the effective parameters on properties of friction stir welds as well as realizing their influence on the weld properties [9], [10], [11], [12]. The influence of some of important parameters such as tool rotation speed (N), welding speed (S) and axial force (F) on weld properties have been investigated. In this investigation, an attempt has been made to relate the optimized friction stir welding process parameters and base material properties of cast aluminium–silicon alloys. This will pave way to predict the optimized friction stir welding process parameters to get defect free joints and to attain maximum tensile strength from the known base material properties [13].
Section snippets
Experimental work
Castings of aluminium–silicon based alloys of A319, A356, and A413 were made by sand casting method and they were machined to rectangular plates of size 175 mm × 75 mm × 6 mm. The chemical composition and mechanical properties of base metals are presented in Table 1, Table 2 respectively. As-cast base metals were used for the experimental work. The initial joint configuration was obtained by securing the plates in position using mechanical clamps. Single pass welding procedure was used to fabricate
Results
In fusion welding of aluminium alloys, the defects like porosity, slag inclusion, solidification on cracks, etc. deteriorates the weld quality and joint properties. Usually, friction stir welded joints are free from these defects since there is no melting takes place during welding and metals are joined in the solid state itself due to the heat generated by the friction and flow of metal by the stirring action. However FSW joints are prone to other defects like pin hole, tunnel defect, piping
Establishing relationships
From the macrostructural analysis, microstructural analysis and tensile strength of the FSW joints, it is found that the process parameters have profound effect. Most of the recent investigations, the FSW process parameters are being selected by trial and error to fix the working range to get defect free welds. The welding conditions and parameters are not same because of the change in the mechanical properties of base metals. The important mechanical properties which control the plastic
Discussion
From the relationships (1), (2), (3), (4), (5), (6), it is found that the FSW process parameters are greatly influenced by the properties of base metals which in turn due to the heat input generated during FSW. The heat input during FSW is calculated by the following expression [18].
q = (2π/3S) μ F N R η,
q = Heat input (kJ/mm),
S = Welding speed (mm/min),
F = Axial force (kN),
N = Tool rotation speed (rpm),
R = Tool pin radius (m),
μ = Coefficient of friction, and
η = Welding efficiency.
The heat input is directly
Conclusions
From this investigation, the following important conclusions are derived:
- (i)
The tensile strength and hardness of the cast aluminium alloys play a major role in deciding weld quality of FSW joints.
- (ii)
The empirical relationships established in this investigation can be effectively used to predict the optimum FSW process parameters to fabricate defect free joints with high tensile strength from the known base metal properties of cast aluminium alloys.
Acknowledgements
The authors are grateful to the Centre for Materials Joining & Research (CEMAJOR), Department of Manufacturing Engineering, Annamalai University, Annamalainagar, Tamil Nadu for extending the facilities of Metal Joining Laboratory and Materials Testing Laboratory to carryout this investigation.
References (19)
- et al.
Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy
Mater Sci Eng A
(2007) - et al.
Effect of welding parameters on mechanical and microstructural properties of AA6056 joints produced by friction stir welding
J Mater Process Technol
(2006) - et al.
Effect of friction stir processing on the microstructure of cast A356 aluminum
Mater Sci Eng A
(2006) - et al.
Three defect types in friction stir welding of aluminum die casting alloy
Mater Sci Eng A
(2006) - et al.
On the role of axial load and the effect of interface position on the tensile strength of a friction stir welded aluminium alloy
Mater Des
(2008) - et al.
The improvement of mechanical properties of friction-stir-welded A356 Al alloy
Mater Sci Eng A
(2003) - et al.
Effect of welding parameters on tensile properties and fracture behavior of friction stir welded Al–Mg–Si alloy
Scripta Mater
(2007) Relationship between base metal properties and friction stir welding process parameters
Mater Sci Eng A
(2008)- et al.
Friction stir welding and processing
Mater Sci Eng R
(2005)
Cited by (35)
Friction stir welding of cast aluminum alloy (A319): Effect of process parameters
2022, Materials Today: ProceedingsPrediction of relationship between angular velocity to the pitch line velocity (ω/v) on tensile strength of friction stir welded AA2014-T6 Aluminium alloy joints: Angular velocity to pitch line velocity ratio on FSW joints
2021, Forces in MechanicsCitation Excerpt :Furthermore, analyzed the effect of FSW parameters on strength of AZ31 B alloy. Jayaraman et al., [10] developed a relationship to attain maximum strength of FSWeld cast aluminum alloy. The welding speed, tool rotational speed and axial force were the important factor to decide weld quality.
Heterogeneous local straining behavior under monotonic and cyclic loadings in a friction stir welded aluminum alloy
2019, International Journal of FatigueFormability analysis of dissimilar friction stir welded AA 6061 and AA 5083 blanks by SPIF process
2019, CIRP Journal of Manufacturing Science and TechnologyCitation Excerpt :The strength and ductility of the weld line were lower than the base metal (BM) in all the combinations. Jayaraman et al. [11] considered the effects of rotational and traverse speeds of the tool on the tensile strength and hardness of the FSW joints of cast aluminum sheets 319, 356 and 413. They suggested some empirical relationships for the optimum tool rotation and welding speeds which results in the defect-free welds with high ultimate strength.
Bending Strength Evaluation of Friction Stir Welded AA6101-T6 and AA6351-T6 Aluminum Alloys Butt Joint
2018, Materials Today: ProceedingsMicrostructure characterization and mechanical properties of gas tungsten arc welded cast A356 alloy
2015, Transactions of Nonferrous Metals Society of China (English Edition)