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The microstructural changes and corrosion response of Resoloy®, a resorbable Mg-Dy-based alloy, are the focus of this study. Hardness, tensile and compressive, and bending tests are used to monitor the changes in the mechanical properties of this material. The corrosion behavior is investigated by stress corrosion of C-rings. Hot-extruded tubes are solution heat-treated at different temperatures and times. The as-extruded condition shows a homogeneous fine-grained microstructure with matrix long-period stacking-ordered (LPSO) structures. Heat treatment at low temperatures and for short times does not significantly change the microstructure but reduces the hardness. Solution heat treatment at relatively high annealing temperatures and long annealing times causes grain growth, resulting in reduced hardness. The microstructure becomes inhomogeneous, medium-sized grains grow, the matrix LPSO structures dissolve, and small bulk LPSO phases develop. The matrix LPSO structures have a positive effect on the corrosion behavior. In particular, the short-term annealing condition shows the most uniform corrosion morphology. Resoloy® is not free of pitting corrosion, but none of the samples fails by cracking. [ABSTRACT FROM AUTHOR]

The effect of second phases on the creep behavior of Mg-Ca-Zr alloys was investigated. Casting and hot-extrusion processes were performed to prepare Mg-xCa-0.5Zr (x = 0 wt.%, 0.3 wt.% and 0.6 wt.%) alloys with different morphologies and distributions of second phases. The as-cast microstructures of Mg-Ca-Zr alloys consisted of an Mg matrix and coarse Mg2Ca intermetallic compounds distributed at the grain boundaries. The hot-extruded microstructures exhibited finer Mg2Ca spherical particles and precipitates distributed homogeneously inside the matrix and along the grain boundaries. The results of creep tests suggested that the viscous glide of dislocation and dislocation climb were the dominant creep mechanisms of Mg-Ca-Zr alloys crept at 200°C. The creep property was strongly related to the morphology and distribution of the Mg2Ca phases. The finer and more homogeneously distributed particles showed a better strengthening effect than the coarser intermetallic compounds distributed along the grain boundaries. [ABSTRACT FROM AUTHOR]

Precipitation hardening in Mg-Y-Nd alloys (WE-type) is based on finely dispersed particles offering an effective strengthening mechanism to achieve high strength at moderate ductility. However, these particles often affect corrosion by being more noble than the matrix. Biodegradable implant materials should show a corrosion rate fit to its application but should be free of pitting corrosion. Especially deep and narrow pits act as notches and cause increased mechanical stress leading into early failure. WE43 has already shown to have an acceptable biological response. In this study, two Mg-Y-Nd-Gd-Dy alloys, WE32 and WE33, in extruded, solution and precipitation heat-treated conditions have been investigated. The difference in alloy composition is not very high. Solution heat treatment (T4) causes grain growth and strength loss. The ageing response to peak hardness depends on the temperature. A rather short ageing response was observed for 250°C, and highest hardness has been found for 200°C at longer ageing time but higher hardness compared to 250°C. Grain growth during ageing is not significant. The higher alloyed alloy WE33 shows better mechanical strength, but less ductility. Corrosion was evaluated with immersion and potentiodynamic polarization in Ringer Acetate solution. The corrosion rate strongly depends on the alloy and heat-treatment condition as well as on the test method. The highest corrosion rate is observed in the solution-treated condition. The peak aged alloy shows the lowest corrosion rate, but non-uniform corrosion and has been evaluated by the pitting factor. [ABSTRACT FROM AUTHOR]

As-cast Mg5Nd, Mg5Nd3Zn, Mg5Nd5Zn and Mg5Nd7Zn alloys were investigated with in situ synchrotron radiation diffraction during compression at 350°C. The results and the post-mortem microscopy investigations suggest that twinning was active during deformation, and was most pronounced in the binary alloy whereas in the ternary alloys grain rotation could be observed. Sub-grain formation could be detected in all the alloys. The reinforcing capacity of the intermetallic network was the largest in Mg5Nd and Mg5Nd3Zn. [ABSTRACT FROM AUTHOR]

Mg-3Sn-2Ca (TX32) alloy has good creep resistance but limited workability. Minor amounts of Al and Si have been added to TX32 for improving its hot workability. The processing map for the TX32-0.4Al-0.4Si alloy exhibited two workability domains in the temperature and strain rate ranges: (1) 310-415°C/0.0003-0.003 s and (2) 430-500°C/0.003-3 s. The alloy exhibited flow instability at temperatures < 350°C at strain rates > 0.01 s. The alloy has been forged to produce a cup shape component to validate these findings of processing map. Finite-element (FE) simulation has been performed for obtaining the local variations of strain and strain rate within the forging. The microstructures of the forged components under the optimal domain conditions revealed dynamically recrystallized grains, and those forged in the flow instability regime have fractured and exhibited flow localization bands and cracks. The experimental loadstroke curves correlated well with those obtained by FE simulation. [ABSTRACT FROM AUTHOR]

Precipitation hardening is an effective strengthening mechanism to achieve high strength at moderate ductility in Mg-RE alloys. However, improved mechanical properties by precipitates that strengthen the alloy can affect corrosion rates as the finely dispersed particles are often more noble than the matrix. Biodegradable implant material should show a certain corrosion rate, but should be free of pitting, because wide and deep pits are notches that can cause higher stress concentration. WE43 has generally shown an acceptable biological response. In this study, a Mg-Y-Nd-Gd-Dy (WE32) alloy in extruded, solution and precipitation heat-treated conditions has been investigated. Solution heat treatment causes grain growth and strength loss. A rather short ageing response to peak hardness was observed, where peak hardening causes hardness values to exceed that of the initial extruded condition. Grain growth during ageing is not significant. Corrosion was evaluated with potentiodynamic polarization in Ringer Acetate solution. The highest corrosion rate was observed in the T4 condition. The peak aged alloy showed the most homogenous form of corrosion. [ABSTRACT FROM AUTHOR]

Magnesium alloys are generally not age hardened due to low age-hardening response. Recent work shows that microalloying may be a path to develop high-strength precipitation-hardening magnesium alloys. Here, we provide examples where microalloying has been used to enhance the age-hardening response through an increase in number density and through modification of the precipitate orientation. Some important considerations when selecting microalloying elements for future alloy development are also discussed. [ABSTRACT FROM AUTHOR]

The effect of homogenization on the hot deformation behavior and texture evolution of Mg-3Sn-2Ca (TX32) alloy is investigated. The cast-homogenized alloy samples were hot compressed in the temperature and strain rate ranges of 300-500 °C and 0.0003-10 s, respectively, and a processing map has been developed by using the flow stress data. The map revealed two dynamic recrystallization (DRX) domains with a peak efficiency of 44% at 360 °C/0.0003 s (Domain 1) and 43% at 485 °C/0.1 s (Domain 2). When compared with the map for as-cast condition, it is observed that both the domains moved towards higher temperatures although the shift of Domain 1 is more noticeable. The apparent activation energy values in the two domains and the regime of flow instability are nearly unchanged by homogenization, suggesting that MgCa and CaMgSn particles in the microstructure are thermally stable. Specimens deformed under conditions in Domain 1 have high Schmid factors for {0001} $$\left\langle {11\bar 20} \right\rangle$$ basal slip and $$\left\{ {1\bar 100} \right\}$$ $$\left\langle {11\bar 20} \right\rangle$$ prismatic slip, while in Domain 2 the deformation progressed due to $$\left\{ {11\bar 2 \bar 2} \right\}$$ $$\left\langle {11\bar 2 \bar 3} \right\rangle$$ second-order pyramidal slip. [ABSTRACT FROM AUTHOR]

The effect of Al (0.4 and 1 wt%) addition on the hot deformation behavior of the Mg-3Sn-2Ca (TX32) alloy has been studied with the help of processing maps generated in the temperature and strain rate ranges of 300-500 °C and 0.0003-10 s. The deformed specimens have been examined as regards changes in texture and microstructure using electron back scatter diffraction and transmission electron microscopy, respectively. The map for the TX32 base alloy exhibited two dynamic recrystallization (DRX) domains in the temperature and strain rate ranges: (1) 300-350 °C and 0.0003-0.001 s, and (2) 390-500 °C and 0.005-0.6 s. While 0.4 wt% Al addition to TX32 did not result in any significant change in the processing map, the map for the alloy with 1 wt% Al (TX32-1Al) exhibited four domains in the ranges: (1) 300-325 °C and 0.0003-0.001 s, (2) 325-430 °C and 0.001-0.04 s, (3) 430-500 °C and 0.01-0.5 s, and (4) 430-500 °C and 0.0003-0.002 s. In the first three domains, DRX has occurred, whereas in the fourth domain, grain boundary sliding takes place causing intercrystalline cracking in tension. In Domain 1 for all the alloys, DRX has occurred predominantly by basal slip and recovery by climb as confirmed by the resulting basal texture and tilt type sub-boundary structure. In Domain 2 of the base alloy and Domain 3 of the alloy with 1 wt% Al, second-order pyramidal slip dominates associated with cross-slip which randomizes the texture, and forms tangled dislocations and twist type sub-boundaries in the microstructure. The addition of 1 wt% Al causes solid solution strengthening and results in Domain 2 of the map of TX32-1Al alloy and in this domain basal+prismatic slip dominate. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of as-cast Mg-4Sn-2Ca (TX42) alloy has been studied using compression tests in the temperature range of 300°C to 500°C, and strain rate range of 0.0003 s to 10 s. Based on the flow stress data, a processing map has been developed, which exhibited two domains of dynamic recrystallization in the temperature and strain rate ranges: (I) 300°C to 380°C and 0.0003 s to 0.001 s, and (II) 400°C to 500°C and 0.004 s to 6 s. While hot working may be conducted in either of these domains, the resulting grain sizes are finer in the first domain than in the second. The apparent activation energy values estimated by kinetic analysis of the temperature and strain rate dependence of flow stress in the domains 1 and 2 are 182 kJ/mol and 179 kJ/mol, respectively. Both the values are much higher than that for self-diffusion in pure magnesium, indicating that the thermally stable CaMgSn particles in the matrix cause significant back stress during the hot deformation of this alloy. The alloy exhibits a regime of flow instability at lower temperatures and higher strain rates, which manifested as flow localization. [ABSTRACT FROM AUTHOR]

Hot deformation behavior of as-cast TX32 (Mg-3Sn-2Ca) alloy has been studied in uniaxial compression in the temperature and strain rate ranges of 300-500 °C and 0.0003-10 s with a view to characterize the evolution of microstructure and texture. On the basis of the temperature and strain rate dependence of flow stress, a processing map has been developed and the crystallographic orientation information on the deformed specimens has been obtained from electron back scatter diffraction micro-texture analysis. The processing map revealed two domains of dynamic recrystallization in the temperature and strain rate ranges of (1) 300-350 °C and 0.0003-0.001 s and (2) 390-500 °C and 0.005-0.6 s. Specimens deformed at peak in Domain 1 exhibited maximum intensity of basal poles located at about 35-45° to the compression axis while those deformed at peak in Domain 2 showed near-random texture. Schmid factor analysis of different slip systems operating in the two domains suggests that basal + prismatic slip causes the basal texture in Domain 1 while second-order pyramidal slip randomizes the texture in Domain 2. [ABSTRACT FROM AUTHOR]

viscoplastic stress model is used to predict contraction forces measured during casting of two binary Mg-Al alloys. Force measurements from castings that did not hot tear, together with estimates from data found in the literature, are used to obtain the high-temperature mechanical properties needed in the stress model. In the absence of hot tearing, the simulation results show reasonably good agreement with the measurements. It is found that coherency of the semisolid mush starts at a solid fraction of about 0.5 and that the maximum tensile strength for the Mg-1 and 9 wt pct Al alloys at their final solidification temperatures is 1.5 and 4 MPa, respectively. In the presence of hot tearing, the measured stresses are generally overpredicted, which is attributed to the lack of a fracture model for the mush. Based on the comparison of measured and predicted stresses, it is also shown that coupling of the stress model to feeding flow and macrosegregation calculations is needed in order to accurately predict stresses in the presence of hot tearing. [ABSTRACT FROM AUTHOR]

Magnesium alloy-based hybrid composites with carbon-fiber, SiCp, and in-situ Mg2Si reinforcements have been prepared by the squeeze-infiltration technique. The results of the studies done on the measurement of the coefficient of thermal expansion after thermal cycling of these composites show that the thermal cycling initially leads to rapid linear expansion of the composite. However, the expansion becomes stabilized after a few cycles, pointing toward formation of the stable interfaces due to the formation of stable precipitates. The model for the growth kinetics of these precipitates at the interface shows a rapid initial growth of the precipitates with the number of thermal cycles, which becomes saturated after a few thermal cycles. The thermal treatment of the composite lowers the coefficient of linear thermal expansion, which can be explained on the basis of further stabilization of the interfaces after the thermal treatment. [ABSTRACT FROM AUTHOR]

Mg-rare earth alloys have improved yield strength and creep resistance compared to commercial alloys such as AZ91, AM60 or AS21. The influence of Zn additions in Mg-Nd alloys on intermetallic phases and the resulting changes in the macroscopic mechanical behaviour of the materials are not yet fully understood. The aim of this work is to identify the effect of Zn additions on the nature of the intermetallic phases and on the mechanical properties in a Mg-4Nd (wt%) alloy. The addition of 8 wt% Zn to a base Mg-4Nd wt% alloy marginally improved the tensile and compression properties at room temperature or at 200 °C with the exception of the 0.2% proof stress of Mg-4Nd-8Zn alloys when tensile- or compression-tested at 200 °C. Two intermetallic phases, a quasi-binary Mg3(Zn, Nd) and ternary Mg50Nd8Zn42, have been identified by the means of electron microscopy and synchrotron diffraction. These results indicate that there are some discrepancies in the current thermodynamic calculations, suggesting an update to the databases may be required. [ABSTRACT FROM AUTHOR]