Abstract: The Mg-rich corner of the equilibrium phase diagram of the Mg-Zn-Gd system has been calculated in detail using the phase diagram calculation software PANDAT and the thermodynamic database for Mg alloys. The calculated phase diagram includes the liquidus projection, isothermal sections and vertical sections. It is found that an increase of Zn content in the Mg-Gd alloy reduces the phase field of α-Mg + GdMg5. Based on the calculated phase diagrams, two alloys, Mg-5.5Zn-2Gd-0.5Zr and Mg-1.6Gd-5.5Zn-0.5Zr (wt.%), denoted as ZGK620 and ZGK616, were developed and their solidification and precipitation processes were analyzed in detail. The optimized thermal mechanical processing and heat-treatment processes were defined by referring to the calculated phase diagrams of the Mg-Zn-Gd system.
Abstract: Most traditional aluminium casting alloys are based on the aluminium-silicon eutectic system because of its excellent casting characteristics. However, the solidus in this system does not exceed 577 °C and the major alloying elements used with silicon in these alloys have high diffusivity in aluminium. Therefore, while these elements enhance the room temperature strength of the alloy, they are not useful at elevated temperatures. Considering nickel-base superalloys, whose mechanical properties are retained up to temperatures that approach 75% of their melting point, it is conceivable that castable aluminium alloys can be developed on the same basis so that they are useful at temperatures approaching 300 °C. In this publication, we present the thought process behind developing a new castable aluminum alloy that is designed specifically for such high temperature applications and we present the alloy’s measured castability characteristics and its elevated temperature tensile properties.
Abstract: The possibility of using alloys of the Al-Cu-Mn-Zr system for obtaining cold rolled sheets directly from cast billets (without homogenization) was investigated. The experimental (SEM, TEM, DSC, mechanical tests, etc.) study and Thermo-Calc software simulation were used for alloy composition optimization. It was shown that optimal structure could be developed in alloys of the following compositional range: 1–2% Cu, 1–2% Mn and 0.2–0.6% Zr. The proposed range of compositions can be recommended for development of new aluminium wrought alloys, which will have two main advantages compared with the commercial alloys of the AA2219 type: i) high tolerance to heating up to 300 °C because of the high amount of Al3Zr and Al20Cu2Mn dispersoids; ii) energy efficient processing, in particular due to the elimination of homogenization, solution treatment and quenching.
Abstract: Additions of rare earth elements to magnesium alloys are qualitatively reported in the literature to retard recrystallisation. However, their effect in the presence of other (non-rare earth) alloy additions has not been systematically shown nor has the effect been quantified. The microstructural restoration following the hot deformation of Mg-xZn-yRE (x = 2.5 and 5 wt.%, y = 0 and 1 wt.%, and RE = Gd and Y) alloys has been studied using double hit compression testing and microscopy. It was found that, in the absence of rare earth additions, increases in zinc level had a negligible influence on the kinetics of restoration and the microstructure developed both during extrusion and throughout double hit testing. Adding rare earth elements to Mg-Zn alloys was found to retard restoration of the microstructure and maintain finer recrystallised grains. However, in the Mg-Zn-RE alloys, increasing the zinc concentration from 2.5 wt.% to 5 wt.% accelerated the restoration process, most likely due to a depletion of rare earth elements from solid solution and modification of the particles present in the matrix.
Abstract: Titanium significantly improves the mechanical properties, especially the ductility of a diecast Al5Mg1.5Si0.6Mn alloy. When a titanium addition of 0.20 wt.% is made the elongation in the as-cast condition is increased from 11% to 18% and the yield strength is increased from 136 MPa to 157 MPa and the ultimate tensile strength from 296 MPa to 308 MPa. The improved mechanical performance can be attributed to the reduced tendency for hot tearing due to Ti addition.
Abstract: Microstructure, mechanical and corrosion properties of Mg-10Gd-2Zn and Mg-10Gd-6Zn (all in wt.%) were evaluated in the as-cast condition. The microstructures of both alloys contained (Mg, Zn)3Gd phase at the interdendritic regions and long period stacking ordered (LPSO) phase distributed in the matrix. The Mg-10Gd-6Zn alloy consisted of a high volume fraction of (Mg,Zn)3Gd intermetallic phases continuously distributed along the grain boundaries. The tensile properties, especially the elongation to failure of the Mg-10Gd-6Zn alloy were slightly lower than those of Mg-10Gd-2Zn. An enhancement in creep resistance was observed with Mg-10Gd-2Zn alloy with the post creep tested microstructure showing dynamic precipitation. Corrosion studies indicated that increased Zn content, from 2 to 6 % in Mg-10Gd alloys, significantly reduced the corrosion resistance.
Abstract: In the present investigation, the effect of addition of Al and small amounts of Ca as well as the effect of heat treatment has been investigated on microstructure, tensile properties and corrosion behaviour of Mg-6Zn alloy produced by squeeze casting. The Mg-6Zn-1Al (ZA61) alloy consisted of α-Mg grains and MgZn (β) phase at the grain boundaries with a much higher strength and ductility than pure Mg. The addition of 0.1 and 0.5 wt% Ca to the ZA61 alloy refined the grain size and increased the volume fraction of the grain boundary phase but did not change the nature of the phase. Consequently, strength increased without much reduction in ductility. The increase in Al content of the alloy to 4 wt% (ZA64) changed the grain boundary phase to Al5Mg11Zn4 (Φ) phase, increased its volume fraction and refined the grain size as compared to ZA61 alloy. Consequently, strength increased with a reduction in ductility. On heat treatment of ZA61+0.5Ca and ZA64 alloys, the volume fraction of grain boundary phases decreased, fine precipitates were obtained in the matrix and the grain size increased. Thus, higher strength with a lower ductility was obtained on heat treatment but the ductility of both the alloys was still higher than that of pure Mg. Thus, 130 MPa 0.2%PS, 225 MPa UTS and 4.9% elongation to fracture could be obtained for the squeeze cast ZA64 alloy in the T6 condition, which are very good tensile properties for a cast Mg alloy. Increase in Al content and heat treatment reduced the corrosion resistance and addition of Ca improved it. The highest corrosion rate was observed to be 0.85 mm/year for the ZA64 alloy in the T6 condition.
Abstract: To develop an aluminium alloy which may combine high thermal conductivity and good castability and anodizability, Al-(0.5~1.5)Mg-1Fe-0.5Si and Al-(1.0~1.5)Si-1Fe-1Zn alloys were assessed as potential candidates. The alloys exhibited 170~190% thermal conductivity, 60~85% fluidity, and equal or higher ultimate tensile strength compared to those of ADC12 alloy.
Abstract: The addition of the rare earth metal Lanthanum to (α+β)-Titanium alloys like Ti 6Al 4V or Ti 6Al 7Nb improves their machinability as short chips form during machining. In related alloys, metallic Lanthanum is distributed as micrometer-size particles which are mainly located at the grain boundaries. In case Iron is present in Lanthanum containing (α+β)-Titanium alloys, a more homogeneous particle distribution is observed leading to improved ductility at room temperature and elevated temperature compared to Iron-free alloys. In the present study, the influence of Iron on the Lanthanum particle size and distribution was investigated in the system Ti 6Al 7Nb xFe 0.9La. First, the solidification behaviour was simulated. Afterwards, alloys with different amounts of Iron (0.25 %, 0.5 % and 1.0 %) were produced. The microstructure of these alloys as well as their deformability and mechanical properties at room temperature were analyzed which were improved compared to the Iron-free Ti 6Al 7Nb 0.9La and Ti 6Al 4V 0.9La alloys.