Gaetano Corrado

Investigation and Optimization of Laser Welding of Ti-6Al-4 V Titanium Alloy Plates

Titanium alloys are employed for several applications, ranging from aerospace to medicine. In particular, Ti-6Al-4V is the most common, thanks to an excellent combination of low density, high specific strength and corrosion resistance.Laser welding has been increasingly considered as an alternative to traditional techniques to join titanium alloys. An increase in penetration depth and a reduction of possible welding defects is achieved indeed; moreover a smaller grain size in the fused zone is benefited in comparison to either TIG and plasma arc welding, thus providing an increase in the tensile strength of the welded structures.The aim of this work is to develop the regression model for a number of responses which are crucial for the feature of the joint. The study was carried out on 3 mm thick Ti-6Al-4V plates; a square butt welding configuration was considered employing a disk-laser source. A 3-level factorial plan was hence arranged in a face-centred cubic scheme. The responses were analyzed referring to the governing parameters. Then, an optimization was carried out via statistical tools, in order to find the optimal welding set-up for the alloy under examination.Copyright

Disk-laser welding of Hastelloy X cover on René 80 turbine stator blade

Nickel-base alloys, such as Hastelloy X and René 80, are among the most common ones for aerospace applications, due to their mechanical strength at high temperatures and oxidation resistance properties, although processing for missile and space vehicle applications requires extensive fusion and resistance welding for fastening. Laser welding using a Yb:YAG disk laser in continuous mode emission is investigated in this paper for overlap joining of Hastelloy X plates on René 80 samples resulting from waste turbine blades. An explorative study is carried out in order to find an appropriate processing window as well as discussing bead features and common issues. Special fixtures for clamping have been specifically developed and tested. A 3-factors study with power, welding speed and focus position as governing parameters has been arranged; 2 levels have been chosen for each factor. Geometric features, defects and indications are discussed referring to the parameters main effects.

Effect of Defocusing on Bead-on-Plate of Ti6Al4V by Yb:YAG Disk Laser

In this study bead-on-plate tests on 3 mm-thick Ti6Al4V sheets were performed using a Yb:YAG thin disk laser in continuous mode to evaluate the effects of focus position on the bead characteristics. Among the various solid-state lasers, the disk laser has better beam quality than conventional rod geometries thanks to the absence of thermal lensing effect. An experimental plan was conducted using nine focus positions with constant power and welding speed. The beads were characterised in terms of geometry, defects, hardness and microstructure. This work is a preliminary study to select the best values of the focal position for subsequent butt welding tests. Analysing the results obtained, the best value of defocusing was -4 mm because, among full penetrated beads, it showed lower undercut and excessive penetration, lower melted area and smaller grain size in the melted area.

Mechanical properties of Inconel 718 in additive manufacturing via selective laser melting: An investigation on possible anisotropy of tensile strength

Possible anisotropy resulting from Additive Manufacturing of metals is investigated. Superalloy Inconel 718 is considered and a number of specimens are manufactured by means of Selective Laser Melting, with different direction of growing. Tensile testing both at room and elevated temperature are conducted.

Characterization of disk-laser dissimilar welding of titanium alloy Ti-6Al-4V to aluminum alloy 2024

Both technical and economic reasons suggest to join dissimilar metals, benefiting from the specific properties of each material in order to perform flexible design. Adhesive bonding and mechanical joining have been traditionally used although adhesives fail to be effective in high-temperature environments and mechanical joining are not adequate for leak-tight joints. Friction stir welding is a valid alternative, even being difficult to perform for specific joint geometries and thin plates. The attention has therefore been shifted to laser welding. Interest has been shown in welding titanium to aluminum, especially in the aviation industry, in order to benefit from both corrosive resistance and strength properties of the former, and low weight and cost of the latter. Titanium alloy Ti-6Al-4V and aluminum alloy 2024 are considered in this work, being them among the most common ones in aerospace and automotive industries. Laser welding is thought to be particularly useful in reducing the heat affected zones and providing deep penetrative beads. Nevertheless, many challenges arise in welding dissimilar metals and the aim is further complicated considering the specific features of the alloys in exam, being them susceptible to oxidation on the upper surface and porosity formation in the fused zone. As many variables are involved, a systematic approach is used to perform the process and to characterize the beads referring to their shape and mechanical features, since a mixture of phases and structures is formed in the fused zone after recrystallization.

Regression modeling to predict the geometrical features of Ti6Al4V thin sheets butt joints welded by disk laser

The aim of this work is to investigate the effects of power, welding speed, defocusing on geometric features and on defects of 1 mm Ti6Al4V laser welded butt joints by a new generation disk laser with 2 kW of maximum power. Them active gain is a Yb:YAG disk instead of traditional Nd:YAG rods. Disk geometry allows to keep the nominal beam quality also at high power because there is no thermal lensing effect, typical of rod geometry. A three level Box-Behnken experimental design with three repetitions is carried out for a total of 45 tests. Linear and quadratic regression equations are developed to relate the input factors to the output variables in order to predict the geometric features of butt joints.