Table 2 — Mechanical Properties of AISI 430 at Room Temperature Density Modulus of Tensile Strength Yield Elongation Hardness (g/cm3) Elasticity (GPa) (MPa) Strength (MPa) (%) (HRB) 7.8 200 459 373 22 85 WELDING JOURNAL 43 Padmanaban and Balasubramanian (Ref. 7) studied the selection of FSW tool pin profile, shoulder diameter, and material for joining AZ31B magnesium alloy. They found that the joint fabricated using a 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. Cavaliere and Panella (Ref. 8) investigated the effect of tool position on the fatigue properties of dissimilar 2024–7075 sheets joined by FSW. They measured the variation of tensile strength, total fatigue life, and crack toughness as the function of the rotating tool distance from the weld interface, by moving it on the AA2024 tool advancing side. They suggested that mechanical properties of the welds increase largely with increasing the distance from the weld interface up to 1 mm, after that a sensible drop was observed increasing more such parameter. Chen and Nakata (Ref. 9) searched the effect of tool geometry on microstructure and mechanical properties of friction stir lap welded (FSLW) magnesium alloy and steel. They suggested that the microstructure at the joining interface, failure loads, and fracture locations of the joints varied significantly with the probe length. Zhang et al. (Ref. 10) searched the effect of the shoulder on interfacial bonding during FSLW of thin aluminum sheets using a tool without a pin. They performed their tests on a conventional vertical milling machine without an apparatus to apply a vertical pressure to the workpieces. In this case, the vertical pressure cannot be applied to the workpieces when the worktable stops rising. Therefore, the tool was tilted by 3 deg to enhance the forging effect of shoulder and improve the intimate contact between the top and bottom workpieces. They suggested that the vertical forging effect could be introduced and enhanced by tilting the tool during FSLW using a common vertical milling machine. Rajakumar et al. (Ref. 11) studied the influence of the FSW process and tool parameters on the strength properties of AA7075-T6 aluminum-alloy joints. They suggested that the joint fabricated at a 1400 rev/min tool rotational speed, 60 mm/min welding speed, 8 kN axial force, using a tool with a 15-mm shoulder diameter, and 45 HRc tool hardness, yielded higher strength properties compared to other joints. There are limited studies about the effect of tool angle on FSW. In this study, the effect of tool tilt angle on mechanical performance was investigated. The quality joints with improved mechanical properties can be obtained by the determination of the proper tool tilt angle for the welded joint of AISI 430 ferritic stainless steel (FSS) materials. Materials and Experimental Procedure AISI 430 (X6Cr17, material number 1.4016) ferritic stainless steel was used in this study. The chemical and mechanical properties are shown in Tables 1 and 2. Rectangular butt joint configuration (100 and 200 mm) with 3-mm thickness were fabricated FSW joints using an automatic, vertical, heavy-duty milling machine with 13.5-kW spindle drive motor. The ferritic stainless steel workpiece plates were secured with work-holding fixtures on the machine traverse table. An initial hole with a diameter a little larger than the probe was drilled between the abutting plates at the start of weld joint. Traversing of tool was initiated after a period of time sufficient to plasticize the workpiece material, which was in contact with the shoulder and the probe. Preheating or interpass heating did not take place throughout the process. The shoulder diameter of the tool was 16 mm, and the pin was approximately 5.7 mm in diameter. Although the plates were 3 mm thick, a 2.5-mm pin was used to protect the workbench plate. The tool material, hard metal carbide (WC-Co hard metal identified as K10, which consists of 94% tungsten carbide, 6% cobalt) with equilateral triangle tip profile, as shown in Fig. 1. Tool material (K10) was made up of tungsten carbide with 1650 HV hardness. The tungsten-based tool material has excellent toughness and hardness over a temperature range from ambient to a minimum of 1200°C. The tool angles were changed between 0 and 5 deg in order to observe the tilt effect on the welded joint strength while holding the other parameters constant at 1120 rev/min tool rotational speed; 125 mm/min welding speed; and 3.5 kN axial force. The experimental details are shown in Fig. 2. Fig. 1 — A — Dimensions of the tool (K10); B — photograph of the tool. A B
Welding Journal | January 2013
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