An Innovative Friction Stir Welding Based Technique to Produce Dissimilar Light Alloys to Thermoplastic Matrix Composite Joints

Aluminum sheets can be joined to composite materials with different techniques. Each of them has advantages and weak points over the others. In literature, new techniques and patents are continuously developed to overcome these difficulties. In the paper a new Friction Stir Welding based approach is proposed to mechanically join AA6082-T6 to self-reinforced polypropylene. The aluminum sheet is pre-holed along both the sides of the weld line. A pinless tool generates the heat and pressure needed to activate back-extrusion of the composite. Joints have been produced with varying hole diameter and pitch. The mechanical resistance of the joint has been evaluated and the different failure modes were identified. Finally, a numerical model was set up to study the process mechanics by calculating the distribution of the main field variables, i.e. temperature strain and nodal displacement

Design of continuous Friction Stir Extrusion machines for metal chip recycling: Issues and difficulties

Friction Stir Extrusion is an innovative direct-recycling technology developed for metal machining chips. During the process, a rotating die is plunged into a cylindrical chamber containing the material to be recycled. The stirring action of the die prompts solid bonding phenomena allowing the back extrusion of a full dense rod. One of the main weakness of this technology is the discontinuity of the process itself that limits the extrudates volume to the capacity of the chamber. In order to overcome that limitation, a dedicated extrusion fixture has to be developed, keeping into account the concurrent needs of a continuous machine. The geometry of the die has to ensure proper pressure in the extrusion channel to prompt the extrusion while allowing the continuous loading of fresh charge. Furthermore, the chips entering the chamber have to find proper conditions for the solid bonding to happen. In this study, the design challenges of a continuous Friction Stir Extrusion machine are described and analyzed, giving an insight on the possible solutions using both experimental, numerical analysis, and keeping into account the sensor equipment necessary to monitor the process

Effect of the Sub-Elements Layout on the Electro-Mechanical Properties of High Jc Nb3Sn Wires Under Transverse Load: Numerical Simulations

The brittle intermetallic Nb 3 Sn superconductor is currently being used to develop high field magnets in the framework of the Hi-Luminosity upgrade of the Large Hadron Collider at CERN. Despite its excellent superconductive properties,Nb 3 Sn wires suffer from significant critical current Ic reduction due to the transverse load applied during the magnets’ assembly and energization. In high critical current density ( Jc >1200 A/mm 2 at 15 T, 4.22 K) RRP and PIT Rutherford cables when applying a transverse load of 150 MPa, the Ic (12 T, 4.22 K) is reduced respectively by about 10-15% and 20%. At this level of transverse load, the Ic reduction is practically reversible, and it is due to the strain induced in the superconductor, which reduces its upper critical field Bc2. Because of the Bc2 reduction, at 19 T and 4.22 K, with a load of 150 MPa, the same cables are expected to experience an Ic reduction up to 40%. Further increasing the transverse loads, cracks in the superconductor also start to reduce (irreversibly) the Ic . A dedicated FEM 3D numerical model coupled with a Jc scaling law has been developed to predict the electro-mechanical behaviour of RRP and PIT wires under transverse loads in the reversible regime. By using this model, the effects of different geometrical factors have been studied to identify the key parameters that allow limiting the effect of transverse loads on the Ic reduction under transverse load. In particular, this paper deals with the role of the: production technologies diameter, sub-elements layout, heat treatment and precompression

Aluminium sheet metal scrap recycling through friction consolidation

In the last decades, several direct-recycling techniques have been developed and investigated in order to avoid material remelting, typical of the conventional aluminum alloys recycling processes. Moreover, the remelting step for aluminum recycling is affected by permanent material losses. Solid-state recycling processes have proven to be a suitable strategy to face such issues. Friction Consolidation is an innovative solid state-recycling technology developed for metal chips. During the process, a rotating die is plunged into a hollow chamber containing the material to be processed. The work of friction forces decaying into heat soften the material and, together with the stirring action of the die, enable solid bonding phenomena producing a consolidated metal disc. This technology has been successively applied to metal chips; in this paper, the feasibility of the process to recycle sheet metal scrap is investigated. The quality of the obtained billets is evaluated through morphological observation and hardness measurements

Energy demand reduction of aluminum alloys recycling through friction stir extrusion processes implementation

Aluminum alloys are characterized by high-energy demands for primary production. Recycling is a well-documented strategy to lower the environmental impact of light alloys production. Despite that, conventional recycling processes are still energy-intensive with a low energy efficiency. Also, permanent material losses occur during remelting because of oxidation. Recently, several solid-state recycling approaches have been analyzed; in fact, by avoiding the remelting step both energy and material can be saved and, therefore, the embodied energy of secondary production can be substantially reduced. In this paper, the solid-state approach Friction Stir Extrusion (FSE) is analyzed for aluminum alloys recycling, the primary energy demand of such recycling strategy is quantified. Comparative analyses with both conventional and direct extrusion based processes are developed

A 3D Finite Element Model of the Reversible Critical Current Reduction Due to Transverse Load in Nb3_{3}Sn Wires

For the next generation of high-field accelerator magnets, CERN relies on Nb $_{3}$ Sn Rutherford cables. This material is extremely brittle and its superconducting properties are strongly dependent on the strain state. In the present 16 T magnet designs, transverse pressures exceeding 150 MPa on Nb $_{3}$ Sn Rutherford cables are expected. For these reasons, it is crucial to estimate transverse load effects on cable critical currents (I $_{c}$ ). Measurements at CERN and Twente University show that Nb $_{3}$ Sn Rutherford cables experience already significant reversible I $_{c}$ reduction at 150 MPa. Experiments at the University of Geneva confirm such results at strand level. This paper presents a 3D Finite Element (FE) model that analyses the reversible critical current reduction of a Nb $_{3}$ Sn strand due to transverse loads. In particular, the simulation analyses the behaviour of a 1-mm-diameter Powder-In-Tube (PIT) wire with 192 sub-elements by addressing the complex geometry of the strand without employing any homogenization. The study is based on the COMSOL Multiphysics® software and on a recently developed scaling law that calculates I $_{c}$ as a function of the strain invariants in the Nb $_{3}$ Sn sub-elements. In the end, results are discussed

A numerical model for Wire integrity prediction in Friction Stir Extrusion of magnesium alloys

A numerical model for the prediction of the wire quality produced by the novel direct machining chip recycling technique known as Friction Stir Extrusion (FSE) is presented. Wire microstructure and wire integrity have been predicted by embedding in the code the equations enabling the calculation of the Zener-Hollomon parameter as well as the W parameter of the Pivnik-Plata solid bonding criterion. The proposed model, developed for the AZ31 magnesium alloy using the commercial simulation package DEFORM, is 3D Lagrangian, thermo-mechanically coupled with visco-plastic material behavior. The model was first validated against experimental temperature measurements and then used to predict the main field variables distributions with varying process parameters

Influence of processing parameters and initial temper on Friction Stir Extrusion of 2050 aluminum alloy

Friction Stir Extrusion is an innovative production technology that enables direct wire production via consolidation and extrusion of metal chips or solid billets. During the process, a rotating die is plunged into a cylindrical chamber containing the material to be extruded. The stirring action of the tool produces plastic flow in the extrusion chamber, densifying and heating the charge so that finally, fully dense rods are extruded. Experiments have been carried out in order to investigate the influence of process parameters and initial temper of the base material on the process variables and on the extrudates\u2019 mechanical properties

Mechanical and metallurgical characterization of AA6082-T6 sheet-bulk joints produced through a linear friction welding based approach

In the last decades, new flexible manufacturing processes have been developed to face the demands, by many industrial fields, for highly customized complex functional parts. The peculiar design of these components often overcomes conventional sheet metal and bulk metal forming processes capabilities. In order to face this issue, new hybrid techniques, capable of exploit key advantages of different processes, have to be developed. In this study, a method to obtain sheet-bulk joints, based on the Linear Friction Welding process, is proposed. The feasibility of the technique was investigated through an experimental campaign carried out with varying pressure and oscillation frequency using AA6082-T6 aluminum alloy. The main mechanical and metallurgical properties of the produced joints, including typical material flow defects, were highlighted. It was found that sound hybrid sheet-bulk joints can be produced by the proposed approach. Finally, it was highlighted how the height of the weld center zone plays a key role on the mechanical properties of the produced joints