Effect of Rotational Speed on Static and Fatigue Properties of Rotary Friction Welded Dissimilar AA7075/AA5083 Aluminium Alloy Joints

In this work, rotary friction welding processes of dissimilar AA7075/AA5083 aluminium alloy rods with the diameter of 15 mm were performed at varying rotational speeds, typically 370 to 2500 rpm. The aim of this research is to improve mechanical properties, in particular, strength and fatigue performance of the weld joints. Several experiments including macro and microstructural examinations, Vickers microhardness measurements, tensile tests, fatigue tests and residual stress measurements were carried out. Results showed that at higher rotational speeds, typically 540 rpm or above, the dissimilar AA7075/AA5083 rotary friction weld joints revealed a static fracture in the AA5083 base metal side, indicating that the joint efficiency is more than 100%. It seemed that the best weld joint was achieved at the rotational speed of 1200 rpm, in which the friction heat was sufficient to form metallurgical bonding without causing excessive flash and burn-off. In such a condition, the fatigue strength of the weld joint was slightly higher than AA5083 base metal, but it was lower than AA7075 base metal. It was confirmed that the crack origin is observed at the interface followed by fatigue crack growth towards AA5083 side, and the growth of crack seemed to be controlled by microstructure and residual stress.

Selection of Weld Structure of Bogies Based on Sub-Model

In order to effectively deal with the problems in the allowable fatigue strength data of weld joints of steering structures, it is necessary to carry out comparative tests and analyses according to various structural stress methods and data. Therefore, on the basis of understanding the applied strength standard of bogie welded structure in China, and aiming at the application of weld structural stress at the present stage, this paper constructs the fatigue diagram and S-N curve of Q345 weld seam based on the actual tested structural stress, and starts with the result study.

EXPERIMENTAL INVESTIGATION OF WELD JOINTS BETWEEN SINTERED NB MODIFIED HK30 STAINLESS STEEL AND WROUGHT/CAST STAINLESS STEELS

Very important property of powder metallurgy parts is ability to join to components produced by different manufacturing technologies or dissimilar materials. Properties of powder metallurgy Nb modified HK30 components are highly influenced by conditions applied during sintering. Weldability of sintered components can be improved using favorable sintering conditions. In this regard, effect of sintering parameters on fusion weldability of Nb modified HK30 is presented in this paper. Investigation of weld joints between HK30, produced by different sintering conditions, and cast HK30 stainless steel is performed. In addition, examination of welds between sintered HK30 and wrought 304 stainless steel is also performed. Microstructural examination and hardness testing of fusion zones and heat affected zones were done for different combinations of base material.

Tensile Behaviour of Friction Stir Welded Joints of Different Aluminium Alloys

This paper investigates the outcome of base metals and their temper condition on tensile and fracture behavior of friction stir welds of various work and precipitation hardening aluminium alloys in different tempers (AA1100-O, 5052-H, AA5086-O & H25, AA2024-O & T6, and AA6061-T651). The type and temper of aluminium alloys affected the tensile, and fracture behavior of weld joints. The extent of improvement in tensile properties of welded joints increased with a decrease in hardness (i.e., from T6 or H to O) of base metals. Softening was not observed for welded joints when base metal was in an annealed temper and an opposite trend was observed for hardened tempers ‘H’ and ‘T6’. Fracture location moved towards the weld centre with the change in temper from ‘O’ to ‘H’ and ‘T6’, hardness minima were closer to base metal hardness in the first case than later. The mode of fracture was ductile for all the weld joints except AA2024-T6 and AA 6061-T651. Except for AA2024-T6 and AA 6061-T651, all weld joints had ductile fracture mode.

Ultrasonic Welding of Nickel with Coarse and Ultrafine Grained Structures

Solid state joints of samples of coarse-grained (CG) and ultrafine-grained (UFG) nickel have been obtained for the first time using spot ultrasonic welding (USW). The UFG structure in disk-shaped samples was processed by means of high-pressure torsion (HPT). On the basis of lap shear tests, the optimal values of the clamping force resulting in the highest values of the joint strength are determined. The microstructures in the weld joints obtained at optimal parameters of USW are characterized by scanning electron microscopy. It is shown that during ultrasonic welding of coarse-grained nickel, a thin layer with an UFG microstructure is formed near the weld surfaces. The bulks of sheets retain the CG microstructure, but a significant dislocation activity is observed in these regions. During USW of samples having an UFG initial microstructure, significant grain growth occurs. Fine grains are observed only along the welding interface. An average lap shear strength of 97 MPa was obtained by welding the UFG samples, which was approximately 40% higher than the strength of samples processed by welding coarse-grained sheets (70 MPa). It is concluded that higher strength weld joints can be obtained by using sheets with the UFG structure as compared to the CG sheets.

Time-of-flight diffraction method for joint with linear misalignment

The time-of-flight diffraction (TOFD) method is known as one of the most accurate flaw sizing methods among the various ultrasonic testing techniques. However, the standard TOFD method cannot be applied to weld joints with linear misalignment because of its basic assumptions. In this study, a geometric model of the TOFD method for weld joints with linear misalignment is introduced and an exact solution for calculating the flaw tip depth is derived. Since the exact solution is extremely complex, a simple approximate solution is also derived assuming that the misalignment is sufficiently small relative to the probe spacing and the flaw tip depth. The error in the approximate solution is confirmed to be negligible if the assumptions are satisfied. Numerical simulations are conducted to assess the flaw sizing accuracy of both the exact and approximate solutions considering the constraint of the probe spacing and the influence of the excess metal shape. Finally, experiments are conducted to prove the applicability of the proposed method. As a result, the proposed method is proven to enable accurate flaw sizing of weld joints with linear misalignment.