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Mg–Dy alloys have shown to be promising for medical applications. In order to investigate the influence of ageing treatment on their mechanical and corrosion properties, three Mg– x Dy alloys ( x =10, 15, 20 wt%) were prepared. Their microstructure, mechanical and corrosion behavior were investigated. The results indicate that ageing at 250 °C has little influence on the mechanical and corrosion properties. In contrast, ageing at 200 °C significantly increases the yield strength, and reduces the ductility. After ageing at 200 °C, the corrosion rate of Mg–20Dy alloy increases largely in 0.9 wt% NaCl solution, but remains unchanged in cell culture medium.

In this study sintering of electrochemical conversion products on the surface of AM50 magnesium alloy by the discharges was identified as an essential step in the coating formation in PEO processing. Clay particles were selected as suitable additives because of their relatively low melting point and possible reactions with the substrate–electrolyte conversion products. The comparison of coatings formed in electrolytes with and without particles clearly indicates a complete change in the microstructure. In the standard electrolytes the coatings are crystalline while they are amorphous if particles are present though the energy input (process parameters) was more or less the same. Only the presence and incorporation of the particles into the coating has obviously induced a low temperature reactive liquid phase formation process, reaching a coating composition with glass forming ability which is likely due to the fast cooling by the electrolyte. In contrast, the coating formation in standard electrolytes has to be considered more like a solid phase sintering. However the results clearly indicate that the sintering of reaction/conversion products by the high energy discharges is a very important step in the coating formation and that the sintering by the discharges in PEO processing can be influenced by the use of additives similar to traditional sintering processes.

Microstructure, mechanical and corrosion properties of binary magnesium–dysprosium (Mg-5, 10, 15, 20 wt.% Dy) alloys were investigated for medical applications. In the as-cast condition, the distribution of Dy is quite inhomogeneous. Mg–10Dy alloy exhibits a moderate tensile and compression yield strength, and the best elongation and corrosion resistance. After T4 (solutionizing) treatment, the distribution of Dy becomes homogeneous. The tensile and compression yield strength of all Mg–Dy alloys decreases. The elongation remains unchanged, while the corrosion resistance is largely improved after T4 treatment.

The mechanism of grain refinement was investigated for Mg-Al alloys inoculated with SiC particles. Contrary to the previously reported Al 4C3 hypothesis, the ternary carbide Al2MgC 2 was observed, which has a crystal structure closer to that of Mg than to that of Al4C3. In the centre of the grains, one or more "hillocks" enriched in Al and C were observed. Based on the observed phenomena, a novel mechanism is suggested to explain the grain refinement of Mg-Al alloys with the addition of SiC particles.

Mg-Zn alloys are widely used as wrought alloys such as ZM, ZK and ZE series. They are reportedly to be prone to hot tearing due to the presence of Zn. The present work first evaluates the hot tearing susceptibility (HTS) of binary Mg-Zn alloys using quantitative experimental methods and thermodynamic simulations based on Clyne's model, and then further investigate the addition of aluminum on the HTS in the ternary alloys Mg-Zn-Al. The results show that the curve of the HTS vs. the content of Zn has a typical "λ" shape. With increasing the content of Zn, the HTS increases firstly, reaches the maximum at 1.5% Zn and then decreases again. The addition of Al in Mg-Zn alloys influences the HTS. In the Mg-Zn-Al ternary system, the HTS decreases with the increase of Al content. The curve of the HTS as a function of Zn content in the ternary Mg-Zn-Al system is a little different from that observed in the binary Mg-Zn alloys. Two peaks are obtained: one is approximately at 1.0 to 1.5 wt.% Zn, another at 3.0 wt.% Zn.

Enzymatic digestion, the commonly used method of adipose-derived stromal cells isolation, is time consuming and expensive, especially when applied to large volumes of tissue. In the present study, the characteristics of the cells obtained by adipose tissue explant culture were studied. We found that adipose tissue fragments could adhere onto the growth surface of flasks in a very short time after plating and that fibroblast-like cells migrated from the explants and reached confluence. Morphologic analysis and surface markers expression suggested the mesenchymal origin of the cells derived from adipose tissue explants. After in vitro expansion these cells were successfully induced into adipogenic, osteogenic, and chondrogenic lineages, which demonstrated their multipotency. The high growth rate and colony-forming efficiency of explant-derived cells were similar to those of cells obtained by digestion. Furthermore, explant culture gave higher yield of cells than digestion method after primary culture. The experiment of ectopic adipogenesis in nude mice suggested the prospects for tissue engineering of these cells. In conclusion, we obtained multipotent stromal cells from adipose tissue by explant culture, and this method was simple, time saving, and gave a high yield of cells. Therefore, explant culture can be used as an effective way to isolate adipose-derived stromal cells for tissue engineering.

Enzymatic digestion, the commonly used method of adipose-derived stromal cells isolation, is time consuming and expensive, especially when applied to large volumes of tissue. In the present study, the characteristics of the cells obtained by adipose tissue explant culture were studied. We found that adipose tissue fragments could adhere onto the growth surface of flasks in a very short time after plating and that fibroblast-like cells migrated from the explants and reached confluence. Morphologic analysis and surface markers expression suggested the mesenchymal origin of the cells derived from adipose tissue explants. After in vitro expansion these cells were successfully induced into adipogenic, osteogenic, and chondrogenic lineages, which demonstrated their multipotency. The high growth rate and colony-forming efficiency of explant-derived cells were similar to those of cells obtained by digestion. Furthermore, explant culture gave higher yield of cells than digestion method after primary culture. The experiment of ectopic adipogenesis in nude mice suggested the prospects for tissue engineering of these cells. In conclusion, we obtained multipotent stromal cells from adipose tissue by explant culture, and this method was simple, time saving, and gave a high yield of cells. Therefore, explant culture can be used as an effective way to isolate adipose-derived stromal cells for tissue engineering.

As a gamma-secretase inhibitor, DAPT has been widely used to evaluate the biological behaviors and Notch signaling pathway in various cells. This study was aimed to examine the effects of DAPT on the growth and vitamin D(3) induced osteogenesis in adipose derived stem cells (ASCs). The cells were treated with or without DAPT and induced to osteoblastic lineage in the presence of vitamin D(3). Alizarin red staining and real-time PCR results indicated that the addition of DAPT to vitamin D(3) treatments enhanced osteogenesis in ASCs. According to the fold increase and colony-forming unit assay results, the cells cultured in DAPT exhibited lower proliferation rate than those cultured in control medium. Hey1, expressed in the nucleus of ASCs to act as a transcriptional repressor, was downregulated when Notch signaling was inhibited by DAPT. Whereas the expression of Runx2 increased in the nucleus of osteogenic induced ASCs after DAPT treatment. This study demonstrated that DAPT reduced the proliferation and enhanced the osteogenesis in ASCs via regulation of Notch and Runx2 expression.

An effective zone solidification method has been found to prepare high purity Mg-Y biomaterials. The corrosion and mechanical properties of the purified middle region are improved remarkably compared with common casting method. The average gain size and secondary dendrite space decrease from the top layer to the bottom layer of the ingot. The oxides, defects and precipitates are mainly enriched in the top layer of the ingot under the impulsion of high thermal gradient. These results are in agreement with that simulated by finite elemental method using FLOW-3D software. It is confirmed that the mode of scallop symmetric solidification attributes to the purifying process. This zone solidification method not only contributes to high purity Mg-based biomaterials, but also provides a new approach to prepare high performance Mg alloys.

Hot tearing (or hot cracking) is recognised in the foundry industry as a serious defect. Although it has been investigated for decades, understanding still stands at a qualitative level. In this work, investigations on hot tearing in the binary Mg–1Al (wt-%) alloy have been conducted, using a contraction stress measuring method which shows evidence of good repeatability. The results show that increasing mould temperature decreases hot tearing susceptibility for Mg–1Al due to a decreased cooling rate. The recorded contraction force curves also show that hot cracks initiate under all investigated mould temperatures; however, the crack propagation behaves differently. At lower mould temperatures, the crack propagates very fast, while at higher mould temperatures it propagates slowly. This indicates that a lower cooling rate allows a better chance for the retained liquid to refill the crack. Consequently this leads to partial or complete interruption of crack propagation.

Uniaxial μ-compression tests have been performed on single crystal Mg with a compression direction, an orientation unfavorable for basal slip. Results show that the early stages of deformation proceed via both twinning and dislocation plasticity. Twinning leads to a reorientation of the crystal favorable for basal slip, typically with the aligned with the compression direction. At a critical strain a large strain burst occurs, and is associated with both rapid propagation of the twin and the activation of basal slip within the twin. Such a mechanistic picture of the deformation behavior is revealed through SEM, EBSD and TEM characterization of the deformation structures.

The AE42 magnesium alloy was developed for high pressure die casting (HPDC) from low-aluminum magnesium alloys. In this alloy the rare earth (RE) elements were shown to increase creep resistance by forming AlxREy intermetallics along the grain boundaries. The present work investigates the microstructure of squeeze cast AE42 magnesium alloy and evaluates its hardness before and after heat treatments. The change in hardness is discussed based on the microstructural observations. Some suggestions are given concerning future design of alloy compositions in order to improve high temperature creep properties even further. It is shown that the microstructure of the squeeze-cast AE42 alloy is stable at high temperature 450 °C. The subsequent solution and ageing treatments have a limited effect on the hardness. The weak age-hardening is attributed to the precipitation of small amount of Mg17Al12-phase with the use of about 0.7 wt.% aluminum. The heat treatment to achieve a maximum increase in the hardness is: solution treatment at 450 °C for 5-10 h followed by an ageing treatment at 190-220 °C for about 5 h.

The segregation of primary alloying elements deteriorates the high temperature creep resistance of magnesium alloys. Annealing at high temperatures alleviating their segregations can improve the creep resistance. Present investigation on the effect of segregation of primary alloying elements on the creep response may provide some useful information about how to improve the creep resistance of magnesium alloys in the future.

Intermetallic phases can be found in almost every magnesium alloy. These intermetallic compounds play a very important role in optimizing the microstructure and mechanical properties. The present paper reviews the effects of intermetallics in magnesium alloys mainly based on their stabilities: dissolvable intermetallics at low temperatures and thermal stable intermetallics at elevated temperatures. The effects of intermetallics are discussed in the age hardenable and creep resistant magnesium alloys, separately. Finally, the further investigations are remarked on the intermetallics, including their precipitation processes, crystal structures and crystallographic orientation relations with magnesium matrix. The aim is to supply useful information in developing new wrought and creep-resistant magnesium alloys which will be used in the powertrain at elevated temperatures.

The development of metal matrix composites (MMCs) is one possibility to overcome the disadvantage of poor high temperature creep properties of present magnesium alloys. Short fiber reinforcement improves the high temperature creep resistance of magnesium alloys. Tensile and compressive creep properties of magnesium alloy AE42 (4 wt.% aluminium and 2 wt.% rare earths) reinforced with 20 vol.% alumina (Saffil®) fibers were investigated in the temperature range of 175-300 °C and stress range of 40-140 MPa, respectively. The MMC was manufactured by direct squeeze casting. The materials investigated show different behaviour depending on type of loading. Stress exponents were calculated from the stress dependence of the minimum creep rate in order to find indications for the possible mechanisms of deformation. The need of correcting the stress dependence of the minimum creep rate by a threshold stress was found. Electron microscopy was performed to investigate the fracture surface of a tensile creep specimen.

Short fiber reinforced AlSi12CuMgNi composites find applications as engine components in the automobile industry. The addition of short fibers raises the interfacial reaction between the fiber and the matrix and modifies the matrix microstructure. Reaction products could change the matrix composition and alter the matrix in a physical metallurgical manner, such as the microstructure and ageing behavior. The present work investigated the microstructure in the interfacial regions and in the matrix, as well as the ageing behavior in Saffil®- and Kaowool®-fiber reinforced composites using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, differential thermal analysis and microhardness tests. The effects of reinforcements on the distribution of the alloying elements and on the interfacial reactions were investigated and discussed. The interfacial reaction mechanisms were analyzed based on thermodynamics and kinetics. Finally, the relationship between the interfacial reaction and ageing behavior was discussed. It was shown that the distribution of the alloying elements is affected by the addition of fibers. The degree of interfacial reaction depends on the reinforcement composition. The growth of the reaction products is controlled by the cation diffusion along the new interface between reaction product and fiber. The ageing hardening is weakened due to the depletion of the alloying element magnesium; caused by the interfacial reaction.

This work investigates the hot tearing behavior of Mg-Al and Mg-Zn alloys quantitatively based on the measurement of contraction force using an experimental setup which was developed at MagIC. An emphasis is given on the analysis of typical hot tearing curves to understand the corresponding metallurgical phenomena shown by these curves. The recorded hot tearing curves, i.e. the contraction force vs. temperature or time, contain valuable metallurgical information. They give not only the precise temperature at which the hot tearing initiates, but also depict information about the propagation of hot cracks. Combined with thermodynamic calculations, the critical solid fraction corresponding to the occurrence of hot tearing can be calculated. Further microstructural observations were performed. Several phenomena such as the crack propagation and refilling of cracks, which influence the slope of hot tearing curves, are also discussed.