School of Engineering

Effect of Sr addition on hot deformation characteristics and texture evolution of Mg–1 wt%Mn (M1) alloy
is investigated with hot compression tests. Sr additions of up to 2 wt% to M1 alloy refine the as-cast
microstructure. Flow curves of M1 and M1–Sr alloys have been plotted at 400 ◦C and 0.1/s strain rate
which show softening behavior indicating dynamic recrystallization (DRX). The texture of M1 alloy after
hot compression is strong basal in nature but it weakens with increasing Sr additions. This is attributed
to particle-stimulated nucleation (PSN) of recrystallization, induced by Mg–Sr intermetallics in the hot
deformed microstructure.

This study deals with the microstructural aspects of the deformation behavior in Al–Si–Cu alloy A380. This has been carried out with in-situ tensile testing coupled with EBSD analysis. The alloy specimens having different microstructures with two different secondary dendrite arm spacing (SDAS) of 9 μm and 27 μm were produced by the unique gradient solidification method. The study of misorientation distribution and texture evolution was performed with different tools in EBSD analysis. The texture was not significantly affected by deformation in both types of alloy specimens. With increase in the deformation, the microstructures are characterized by degradation of EBSD patterns and generation of substructures including low angle boundaries (LABs) and high angle boundaries (HABs). In both the microstructures with low and high SDAS, the boundaries were concentrated around eutectic phases; however this behavior was more pronounced at higher SDAS. The increase in the fraction of LABs with deformation was much higher in the microstructure with higher SDAS than with lower SDAS. This localized strain concentration was especially attributed to the large and elongated eutectic Si particles and Fe-rich intermetallics. The lower mechanical properties obtained at higher SDAS are the result of inhomogeneous strain distribution in the microstructure.

Alloys Mg-1% Mn (M1) and Mg-1% Mn-1.6Sr (M1-1.6Sr) were subjected to three extrusion temperatures of 300, 350 and 400°C at 8 mm/s ram speed in order to investigate the texture evolution and recrystallization mechanisms. M1 alloy exhibits weaker texture after extrusion at 300°C, but develops strong basal texture at 350 and 400°C. The weaker texture of M1 at 300°C is partially due to random orientations created by CDRX mechanism. M1-1.6Sr alloy develops weaker textures at all extrusion temperatures as a result of particle stimulated nucleation promoted by Mg-Sr intermetallics which forms grains with random orientations.

Microstructure and texture evolution in Mg-1 %Mn-Sr alloys during extrusion has been investigated. At 350°C, the extrusion of Mg-1 %Mn (M1) alloy exhibits the progressive formation of basal texture from the undeformed zone to the die opening. The extruded microstructure of M1 consists of recrystallized grains nucleated by grain boundary bulging and elongated parent grains along with extensive twinning. At 350°C, the extrusion of M1-1.6Sr alloy results in progressive elongation of Mg-Sr precipitates in the form of stringers from the undeformed zone to the die opening. The final extruded microstructure of this alloy shows extensive recrystallization occurring at the intermetallic stringers by particlestimulated nucleation (PSN). M1-(0.3-1.6)%Sr alloys display weaker textures due to PSN which creates new grains with random orientations. At 250°C, the extrusion of M1 creates necklace of small recrystallized grains around large elongated parent grains. M1-1.6Sr alloy extruded at 250°C exhibits continuous dynamic recrystallization (CDRX) in the Mg matrix and PSN at Mg-Sr precipitates. PSN is less extensive at lower temperature. Both CDRX and PSN grains have random orientations, and therefore, alloy develops random texture.

Magnesium-manganese, M1, alloy is preferred for extrusion applications due to its extrudability. It is mainly used as a sacrificial anode or as a creep resistant alloy at elevated temperatures in the nuclear industry. Since Mn does not provide a significant strengthening effect, the alloy is not considered for structural applications. The basal texture which forms after extrusion orients the basal planes parallel to the extrusion direction causing anisotropy in mechanical properties. This basal texture, as well as the low strength of the alloy are the main challenges in its widespread applications. In this study, the effect of Sr addition on the texture and mechanical properties of M1 alloy was studied. M1-Sr alloys showed weakened texture by developing random texture components during extrusion. The texture randomisation is attributed to particle stimulated nucleation (PSN) around Mg-Sr intermetallics during recrystallisation. M1-Sr compositions are found to show improved strength and ductility as well as reduced yield asymmetry.

Three Mg alloys Mg-1 pctMn (M1), Mg-1 pctMn-1.3 pctSr, and Mg-1 pctMn-2.1 pctSr were subjected to two different extrusion temperatures and two different extrusion speeds in lab-scale extrusion. The extrusion temperatures of 573 K and 673 K (300°C and 400°C) and two ram speeds of 4 and 8 mm/s were used at constant extrusion ratio of 7. M1 exhibited strong basal texture after extrusion at 673 K (400°C) at higher speed. At 573 K (300°C), recrystallization in all alloys takes place completely or partially by continuous dynamic recrystallization mechanism, while particle stimulated nucleation (PSN) occurs in all M1-Sr alloys at both extrusion temperatures and speeds. At 673 K (400°C), grain boundary bulging is the only recrystallization mechanism in alloy M1, while it occurs in combination with PSN in M1-Sr alloys. The effect of texture weakening by PSN is more significant in M1-Sr alloys extruded at 573 K (400°C). The plant extrusion trials were carried out on Mg-1 pctMn, Mg-1 pctMn-0.3 pctSr, and Mg-1 pctMn-2.1 pctSr at 623 K (350°C) with different speeds than in lab-scale extrusion. M1 alloy exhibited strong basal texture at both speeds, while Sr additions of 0.3 and 2.1 pct promoted similar amount of texture weakening.

Al-Si-Cu alloys were cast with the unique gradient solidification technique to produce alloys with two cooling rates corresponding to secondary dendrite arm spacing (SDAS) of ∼9 and ∼27 µm covering the microstructural fineness of common die cast components. The microstructure was studied with optical microscopy and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and electron backscattered diffraction (EBSD). The alloy with higher cooling rate, lower SDAS, has a more homogeneous microstructure with well distributed network of eutectic and intermetallic phases. The results indicate the presence of Al-Fe-Si phases, Al-Cu phases and eutectic Si particles but their type, distribution and amount varies in the two alloys with different SDAS. EBSD analysis was also performed to study the crystallographic orientation relationships in the microstructure. One of the major highlights of this study is the understanding of the eutectic formation mechanism achieved by studying the orientation relationships of the aluminum in the eutectic to the surrounding primary aluminum dendrites.

In this investigation\ attention was focused on the tool stresses that emerge during manufacturing of fasteners[ These stresses were studied both experimentally and theoretically[ The theoretical part comprised _nite!element simulation[ This simulation showed that the zone at the die insert pro_le radius is so heavily loaded that plastic deformation is initiated in this region[ In the experimental part\ the emerging strains were measured in the region close to the interface between the die insert and the stress ring[ The correspondence is good between the theoretical and experimental strains in this region[ In spite of this and although 19 fasteners were cold!forged\ the die insert did not fracture[ Forming at production facilities showed that the die insert cracked after 8979 parts were produced[ The results obtained in this investigation and the test conducted at production facilities indicate that high cycle fatigue\ and not monotonic rupture\ is the main cause of tool fracture in practice[ Þ 0888 Elsevier Science Ltd[ All rights reserved[ Keywords] Cold forging^Heading^Fasteners^Tool stresses^Finite!element analysis^Fatigue

In this investigation, the attention is focused on the springback and fracture of thick stainless steel sheets. Nine different stainless grades and various thicknesses are tested. The thinnest sheet is 7.9 mm, whilst the thickest sheet is 31.3 mm. A consistent analytical model is constructed for prediction of the springback, the inner sheet radius prior to and after unloading, and the smallest die width. The springback calculated by this analytical model is in all cases smaller than that found experimentally. The correspondence between theory and practice is, however, very good, although the shift in the position of the neutral axis and thinning are neglected in the theoretical analysis. Fracture did not occur in any of the conducted bending operations. It is commonly assumed that fracture in v-die air bending is related to the reduction in the cross-section area at fracture, Z, in tensile testing. Z was greater than 70% for the majority of the studied materials. It is shown that particularly the Ž . mode of fracture fracture through shear bands or by necking should be studied in future investigations. ᮊ

The springback of double curved autobody panels is studied theoretically and experimentally. Both steel and aluminium sheets are included in this investigation. The obtained results show that the springback is decreased with increasing binder force, increasing curvature, increasing sheet thickness and decreasing yield strength. This paper comprises also a discussion on the plastic strains and their in#uence on the springback.

The automotive industry has shown a growing interest in tube hydroforming during the past years. The advantages of hydroforming (less thinning, a more efficient manufacturing process etc.) can, for instance, be combined with the high strength of extra high strength steels, which are usually less formable, to produce structural automotive components which exhibit lower weight and improved service performance. Design and production of tubular components require knowledge about tube material behaviour and tribological effects during hydroforming and how the hydroforming operation itself should be controlled. These issues are studied analytically in the present paper. Hydroforming consists of free forming and calibration. Only the so-called free forming is treated here. The analytical models constructed in this paper are used to show what the limits are during the free forming, how different material and process parameters influence the loading path and the forming result, and what an experimental investigation into hydroforming should focus on. The present study was a part of a larger investigation, in which finite-element simulations and experiments were also conducted. The results of these simulations and experiments will be accounted for in coming papers.

CITATIONS 0 READS 75 4 authors, including: Some of the authors of this publication are also working on these related projects: Foundry master 3.0 View project CastMa -Joining of cast and extruded light alloy components View project Nils-Eric Andersson Jönköping University Abstract

The current paper focuses on development of a method for studying micro-scale strains on the microstructure of ferritic cast iron. For this purpose, in-situ tensile tests were done under the optical microscope combined with digital image correlation (DIC). Critical in this development was to be able to achieve a reliable high spatial resolution of strain around microstructural features, such as graphite particles. Measurement of local strain fi elds in cast iron materials have so far been relying on displacement of naturally occurring microstructure patterns such as graphite particles, which limits the spatial resolution of strain measurement. In order to increase the spatial resolution of the measured strain, a pit etching procedure was applied to generate a random speckle pattern on the ferritic matrix. The critical challenges of in-situ investigation of microstructural deformation were identified as speckle pattern quality and accurate selection of subset size and strain window s...

a Corresponding author email: Keivan.Amiri-Kasvayee@jth.hj.se Keywords: Micro-crack, local strain, ferritic cast iron, digital image correlation (DIC), in-situ tensile testing This paper focuses on measuring local strain at micro-crack initiation in fully ferritic cast iron alloys, using micro-scale strain mapping. Strain mapping was achieved using in-situ tensile test under optical microscope combined with digital image correlation (DIC). A previously developed pit etching procedure was used to create microscale random speckle patterns in the microstructure of the tensile specimens. Real-time microscope images were recorded during tensile deformation and analyzed by using DIC technique. Local strain values were measured around early formed micro-cracks during deformation. Results showed a heterogeneous deformation in microscale level. The micro-cracks were initiated at well-defined local strain levels but with large variations in the global strain level. Crack initiation was strongly associated with the graphite particles and their morphology.

Eeffect of Boron addition on the microstructure and mechanical properties of ductile iron, GJS-500-7 grade was studied. Three cast batches with the Boron content of 10, 49 and 131ppm were cast in a casting geometry containing plates with thicknesses of 7, 15, 30, 50 and 75mm. Microstructure analysis, tensile test, and hardness test were performed on the samples which were machined from the casting plates. Addition of 49 ppm Boron decreased pearlite fraction by an average of 34±6% in all the cast plates. However, minor changes were observed in the pearlite fraction by increasing Boron from 49 to 131 ppm. Variation in the plate thickness did not affect the pearlite fraction. The 0.2% offset yield and ultimate tensile strength was decreased by an average of 11±1% and 18±2%, respectively. Addition of 49 ppm Boron decreased Brinell hardness by 16±1%, while 11±2% reduction was obtained by addition of 131ppm Boron.

In this study, the microstructure of resistance spot welds of advanced ultrahigh strength TRIP1100 steel was investigated. For this purpose, welding was performed after determining the best welding parameters. Four sections of the heat-affected zone (HAZ) regions were selected in the regions where the heat exchange was used to control the microstructure. Then, they were used with EBSD by scanning electron microscopy (SEM). The results showed that the TRIP1100 steel microstructure consisted of polygonal ferrites, bainites, residual austenite (RA) and martensite/austenitic islands (M/A). They also showed that the melting zone (FZ) has a lath martensite structure, and the grains are larger in packets. The structure of the martensite and different orientation grains are located in the Upper-critical area (UCHAZ). In the inter-critical region (ICHAZ), the high carbon martensitic content is higher due to the presence and the structure of ferrite and martensite. In the sub-critical region ...