Ultrasonic surface rolling process (USRP) is an effective method to improve material surface quality, such as surface finish, microstructure, and stress state. Previously, USRP is usually used in comparably hard materials (e.g., instance steel and titanium alloys). In this paper, attention is focused on low hardness aluminum alloy which is widely used in the aviation industry. Aluminum alloy 7050-T7451 is used to investigate its surface characteristics in the ultrasonic rolling experiment. With the aid of surface optical profiler, X-ray stress analyzer, scanning electronic microscope (SEM), and energy-dispersive spectrometer (EDS), the differences of surface characteristics are explored in the USRP-treated area and that of the turning area. In addition, the influence of feed rate on surface integrity is also investigated. The results show that surface integrity is improved by USRP, and the best quality is obtained with the feed speed of 0.10 mm/r. Under the optimal experimental condition, surface roughness (Ra) is reduced to 0.059 μm, axial and tangential surface compressive residual stress is increased to −130.6 and −330.8 MPa, respectively, and surface microhardness is increased by 41.3 %. Metal flow traces, fusion of surface grain boundary, and the phenomenon of impurity phase diffusion are observed in the cross section of the treated specimen. The internal strengthening mechanism of the USRP-treated surface is probed.

Study on surface characteristics of 7050-T7451 aluminum alloy by ultrasonic surface rolling process

Surface nanocrystallization plays a great role in the enhancement of global behavior of products In this paper, a theoretical modal for grain refinement of ultrasonic thread root rolling process (UTRR) is explored, and its effect on surface nanocrystallization is investigated by conducting comparative experiments of UTRR and conventional thread root rolling process (CTRR) Various surface analytical techniques, such as transmission electron microscopy, metalloscope, X-ray diffraction, and Vickers hardness tester are then adopted to quantitatively study surface nanocrystallization of different treated specimens The fatigue tests are last performed to evaluate effect of grain refinement on fatigue performance Results show that nanocrystalline is successfully synthesized on thread surface by UTRR, with grain size ranging from 15 to 20 nm, while hardness in top surface is remarkably improved from 580 to 700 HV due to surface nanocrystallization By comparison, only subgrains are generated by CTRR confirming that the ultrasonic technique plays a key role on surface nanocrystallization The result also shows that the increased relative motion distance between roller and surface greatly contributes to nanocrystallizaion for UTRR Fatigue tests show that specimens treated by UTRR achieve the longest fatigue lives, which confirms that nanocrystallization of root surface greatly contributes to the improvement of fatigue performance

Surface nanocrystallization and its effect on fatigue performance of high-strength materials treated by ultrasonic rolling process

In a few last decades, equal-channel angular pressing (ECAP) has been one of the most prominent procedures for fabrication of ultrafine-grained (UFG) structures among various severe plastic deformation (SPD) techniques. The objective of this paper is to experimentally investigate the influence of longitudinal ultrasonic vibrations on the ECAP process. A robust experimental ECAP system was designed and manufactured, in which the punch can be excited by ultrasonic vibrations. ECAP experiments were carried out with and without ultrasonic vibration on pure Al. The microstructure of the specimens formed with ultrasonic-assisted ECAP and conventional ECAP were studied. The results of this study showed that superimposing ultrasonic vibrations on the ECAP process could improve the grain refinement efficiency. The grains of the specimens after conventional ECAP process were refined to 45 μm, while by applying ultrasonic vibration with amplitudes of 2.5 and 5 μm, the grains were refined to 28.2 and 22 μm , respectively. Using higher vibration amplitudes caused more refinement of the grains. The homogeneity of the microstructure after four passes of ECAP was also improved by 26.7 % while using ultrasonic vibration with amplitude of 2.5 μm. Higher vibration amplitudes made a more homogenous structure. The yield strength and ultimate tensile strength of the specimens after one pass of ECAP were higher in comparison with the conventional ECAP.

Improvement of ECAP process by imposing ultrasonic vibrations

Effects of ultrasonic vibration on the compression of pure titanium.

In order to shorten the preparation period, dieless shear spinning is widely used in various industrial fields with advantage of economy of materials and easy control. Controlling roller path is one of the main methods for changing thickness distribution. A new discretization method is proposed by theoretical derivation in dieless shear spinning. It will generate a virtual axis by inclining the flange of the workpiece. And, the roller path is derived for spinning machine combined with the sine law in shear spinning. The derived path should be applied after the range of forming reaches the certain height. The thickness distribution of formed workpiece is basically in agreement with the theoretical value. It also illustrates that roller nose radius and axial feed will influence the surface quality.

A research on thickness distribution of oblique cone in dieless shear spinning

Tube spinning process, also known as flow forming, is one of the manufacturing methods in production of seamless tubes. During the tube spinning process, the workpiece was excited by ultrasonic vibrations. The authors’ last research was focused on variation of forming forces and surface effects of tube spinning parts under ultrasonic vibrations. In the present study, the effects of ultrasonic vibrations on mechanical and metallurgical properties of AA 2024 workpieces were investigated. In fact, different characteristics of the workpiece in the presence and absence of ultrasonic vibrations were evaluated. The results of microstructure and microhardness tests revealed that in the presence of ultrasonic vibrations, precipitate formation was reduced. Also, precipitate shape and distribution through microstructure, particularly near the outer surface up to 2 mm depth, was changed. In addition, applying ultrasonic vibrations not only increased the hardness and the depth of hardened layers but also improved the uniformity of hardness profile across the thickness.

Mohammadali Rasooli

Papers

Investigation of ultrasonic vibration effects on the microstructure and hardness of aluminum alloy 2024 tube spinning parts