Yvonne Durandet

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

Rare-earth metals, particularly neodymium, dysprosium, and praseodymium are becoming increasingly important in the transition to a green economy due to their essential role in permanent magnet applications such as in electric motors and generators. With the increasingly limited rare-earth supply and complexity of processing Nd, Dy, and Pr from primary ores, recycling of rare-earth based magnets has become a necessary option to manage supply and demand. Depending on the form of the starting material (sludge or scrap), there are different routes that can be used to recover neodymium from secondary sources, ranging from hydrometallurgical (based on its primary production process), electrochemical to pyrometallurgical. Pyrometallurgical routes provide solution in cases where water is scarce and generation of waste is to be limited. This paper presents a systematic review of previous studies on the high-temperature (pyrometallurgical) recovery of rare earths from magnets. The features and conditions at which the recycling processes had been studied are mapped and evaluated technically. The review also highlights the reaction mechanisms, behaviors of the rare-earth elements, and the formation of intermediate compounds in high-temperature recycling processes. Recommendations for further scientific research to enable the development of recovery of the rare-earth and magnet recycling are also presented.

Feasibility of measuring residual stress profile in different self-pierce riveted joints

Abstract The feasibility of measuring residual stresses in self-pierce riveted (SPR) joints by neutron diffraction technique was investigated. The main challenge involved dealing with the very small dimensions of SPR joints. Two different joints were examined: aluminium–steel and steel–steel. Even though small dimensions were involved, meaningful results were obtained. In the rivet head, tensile stress was observed for the steel–steel sample, whereas only compressive stress was observed for the aluminium–steel. The residual stress in the rivet head was higher at the centre and lower at the edge for both joints. Stresses in the sheet material beside the rivet wall and at a distance of three times the rivet radius from the rivet axis were not significant. For the SPR joints examined, the maximum value of residual stress was compressive and occurred in the rivet leg. The results are discussed according to the physical events involved during the process.

Characterisation of force–displacement curve in self-pierce riveting

Abstract A systematic study of the force–displacement curve of the self-piercing riveting (SPR) process and associated sample characterisation have been carried out in this work. Carbon steel sheet with three different thicknesses and steel rivets with three different hardness levels have been used to examine their impact on the force–displacement characteristic curve. The force–displacement curve is segmented into four different stages, which give the signature of the quality of the joint depending on different process variables. This study shows that the force–displacement curve can be used to monitor the quality of the joint within the same process parameters (rivet length and hardness, total stack thickness and die geometry).

Characterizing the material properties of a tube from a lateral compression test

Material characterization is essential for finite element analysis (FEA) as the accuracy of the outputs of the simulation depends on the quality of the input material data. Conventional tests such as the uniaxial tensile test and uniaxial compression test have some drawbacks and limitations in characterizing tubular materials. In this paper, an improved methodology to determine the material properties of a tube based on lateral compression testis reported. Mechanical properties such as yield strength and elastic modulus were obtained from lateral compression experimental data. The material work hardening coefficient and work hardening exponent were obtained by inverse finite element analysis (IFEA). The proposed methodology was used to determine the material properties of an aluminium 6060T5 tube, and results were compared with those reported from uniaxial tensile tests. Comparison showed that the proposed methodology could be used to easily and accurately predict the tube material properties based on the lateral compression test.

The Application of Magnesium Alloys to the Lightweighting of Automotive Structures

This paper investigates some of the opportunities for magnesium alloys based on magnesium’s attributes, such as excellent die castability and high strength to weight ratio. Barriers to the uptake of magnesium alloys are considered and recent technical advancements outlined including the development of creep resistant alloys, high extrudibility alloys, joining technologies and corrosion performance. Finally issues to do with the life-cycle performance of magnesium alloys are discussed.

Optimising parameters for meaningful measurement of residual strain by neutron diffraction in self-pierce riveted joints

Abstract The aim of this work is to examine the uncertainties involved in measuring residual strain and their dependence on both the gauge volume of the neutron beam and the acquisition time in self-pierce riveted (SPR) joints while using the neutron diffraction technique. The main challenge involved dealing with the very small dimensions of SPR joints and developing optimum instrument configuration that allowed faster and/or more accurate stress measurement in SPR while maintaining the same time resolution required for the millimetre scale of the problem. Two different gauge volumes were used (0·125 and 1·0 mm3), and two different measuring directions were chosen in order to examine the rotational accuracy of the sample table. All measurements were conducted in steel‐steel joints. Even though small sizes were involved, meaningful results were obtained and measurement errors were reduced by optimising the instrument parameters.

Residual stress profiles in riveted joints of steel sheets

Abstract The residual stress profiles in two different self-piercing riveted (SPR) joints were characterised using the neutron diffraction technique. The joints were produced using semi-tubular steel rivets and carbon steel sheets of different thicknesses and hardnesses. The residual stress in the sheet material inside the bore of the rivet was compressive at the centre and the stress became tensile away from the centre. The stresses found in the semi-tubular rivet were compressive, with a lower magnitude in the rivet head compared with those in the rivet leg. For the SPR joints examined, the compressive residual stress in the rivet leg was greater for the thin joint than the thick joint, and this was due to the higher force gradient encountered during the rivet flaring stage. The originality of this work was to relate the residual stress profile to the physical event that occurred during the SPR process.

Evaluation of Residual Stress in SPR Joint by Neutron Diffraction

The feasibility of measuring residual stresses in Self-Pierce Riveted (SPR) joints by neutron diffraction was evaluated in this study. Despite the small dimensions involved, meaningful results were obtained. It was observed that residual stress in the rivet head was higher in the centre and lower at the edge. For the SPR joints examined, the maximum value of residual stress evaluated was 550MPa, compressive and occurred in the rivet leg. Stresses in material adjacent to the rivet wall and at a distance of three times the rivet radius from the rivet axis were not significant. The results are discussed with respect to the physical events involved during SPR.

Effect of Joining Process on the Coatings of Self-Piercing Rivets

In this study, effects of laser assisted self-pierce riveting (LSPR) as a mechanical joining technique were investigated on the coatings of self- piercing rivets. Zn-Sn and Al plated rivets were used to join magnesium sheets by LSPR. Microstructure, surface topography and roughness of the rivet’s coatings were characterized by optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and surface profilometry. A comparison of results before and after joining process showed that under joining conditions, Zn-Sn coating was deformed during riveting process and its thickness and microstructure varied along the rivet shank, while Al coating remained unchanged and no effects of riveting process was detected.

SPR Characteristics Curve and Distribution of Residual Stress in Self-Piercing Riveted Joints of Steel Sheets

Neutron diffraction was used to describe the residual stress distributions in self-piercing riveted (SPR) joints. The sheet material displayed a compressive residual stress near the joint, and the stress gradually became tensile in the sheet material far away from the joint. The stress in the rivet leg was lower in the thick joint of the softer steel sheet than in the thin joint of the harder steel sheet. This lower magnitude was attributed to the lower force gradient during the rivet flaring stage of the SPR process curve. This study shows how the residual stress results may be related to the physical occurrences that happened during joining, using the characteristics curve. The study also shows that neutron diffraction technique enabled a crack in the rivet tip to be detected which was not apparent from a cross-section.