Volume 62, Issue 7

In this study, AA 5083 and AA 6082 aluminum alloy plates were joined by friction stir welding method at different rotational speeds and traverses. Mechanical tests and metallographic examinations were performed on the joints. In tensile test, welding performance was found to be in the range of 66.23 %–77.27 % compared to the tensile strength of the AA 5083 base alloy, and in the range of 62.22 %–72.59 % compared to the tensile strength of the AA 6082 base alloy. Result of the bending test, splitting was observed at the heat affected zone boundary after surface bending in some parameters. The light microscope examinations, onion ring-shaped shear bands were clearly seen in the center of the welded joints. The hardness values were low on the AA 5083 side, while they tended to increase towards the AA 6082 side.

The relationship between the microstructure of the ring forging and the ultrasonic anomalies were studied in response to the localized anomaly observed during the non-destructive testing of TA15 titanium alloy ring forging. The distribution of internal defects was explored through water immersion ultrasonic testing of ring forging. The microstructure of the normal region and the abnormal zone were compared using scanning electron microscopy and electron backscatter diffraction techniques. And finite-element simulation was used to simulate the formation process of the abnormal ultrasound position. The results showed that the different layers of the ring-forged component exhibited varying degrees of bottom wave attenuation along the radial direction. The abnormal area corresponded to a higher number of primary α-phase and larger grain sizes. Under the combined effect of temperature and stress, the recrystallized grains began to grow abnormally, leading to significant bottom wave attenuation.

This work aims to study the microstructural variations in 2205 duplex stainless steel welded by cold metal transfer. Duplex stainless steels, characterized by their twophase microstructure of austenite and ferrite, exhibit exceptional mechanical properties and corrosion resistance that can be significantly influenced by welding techniques. Plates of 8 mm thickness, solution annealed at 1070 ˚C, were joined using ER 2209 welding wire and a shielding gas mixture of 98 % Argon and 2 % O 2 . Microstructural analysis and ferrite content measurements were performed on the welded specimens. The microstructure was observed using three different electrolytic etchants 45KOH, 10KOH and 40NaOH Results showed that the best contrast of microstructure phases is seen in 45KOH etchant, resulting in dark green ferrite and yellow colored austenite as compared to 10KOH and 40NaOH etchant. Various morphologies of austenite were observed in the weld area. The base metal contains elongated pools of austenite in the ferrite matrix. The heat affected zone shows higher percentage of ferrite phase and the weld region shows highest austenite content with different morphologies like grain boundary Austenite, side plates of austenite or Widmanstätten austenite and intergranular austenite.

Fractured fasteners were received from a large gas turbine engine. The subject bolts are M16 fasteners with rolled threads. They are made of N80A, a wrought precipitationhardenable nickel-base superalloy. This alloy features one of the highest creep strengths among this class of alloys. The fasteners are used to join two large casings in the turbine exhaust duct. The flange of this connection has more than one hundred bolts on the outer diameter, and the same number on the inner diameter. Only six out of those many bolts exhibited creep fractures. All failed bolts sat adjacent to each other on the outer diameter flange in the 12 o’clock position. Five of those fractured bolts were received at the authors’ laboratory. It was concluded that excessive service temperatures and/or higher than intended stresses caused the premature creep failures. An unfavorable microstructure with elephant grains may have contributed to the failures. More details about the assembly situation cannot be provided here.