On the Elevated Temperature, Tensile Properties of Al-Cu Cast Alloys: Role of Heat Treatment

The present study aims to investigate the mechanical properties of a newly developed aluminum Al-6.5% Cu-based alloy, coded HT200, as well as to determine how these properties can be further improved using grain refinement and heat treatment. As a result, the effects of different heat treatments and alloying additions on the ambient and high-temperature tensile properties were examined. Three alloys were selected for this study: (i) the base HT200 alloy (coded A), (ii) the base HT200 alloy containing 0.15% Ti + 0.15% Zr (coded B), and (iii) the base HT200 alloy containing 0.15% Ti + 0.15% Zr + 0.5%Ag (coded C). The properties of the three HT200 alloys were compared with those of 319 and 356 alloys (coded D and E, respectively), subjected to the same heat treatment conditions. The results obtained show the optimum high-temperature tensile properties and Q-values for the five alloys of interest, along with the corresponding heat treatment conditions associated with these properties. It was found that the T6 heat-treated alloy B was the optimum alloy in terms of properties obtained, with values comparable to those of commercial B319.0 and A356.0 alloys.

Ductile Cast Iron with High Toughness at Low Temperatures

High life expectancy of cast components and good material performance at dynamic load are a prerequisite to cater for future trends in wind energy generators. To remain competitive in this ever evolving sector challenges reside in alloy development. In this work fractional factorial design has been applied to ferritic ductile iron with varying contents of silicon (1.6‑2 wt%), nickel (0‑1 wt%), cobalt (0‑3 wt%) and copper (0‑0.2 wt%). The minimum criteria the new alloy should meet were a minimum yield strength of 240 MPa and an impact work of minimal 8 J at a temperature of -20 °C for wall thicknesses of 60‑200 mm. To obtain these mechanical properties thick-walled castings with additional insulation were produced to achieve a higher thermic module. They provided the material for test specimens to perform static tensile tests, Charpy impact tests at varying temperatures and a microstructure analysis. With these results, a sweet spot plot has been created. That way, an optimum alloy composition could be found and has been proven by validation experiment.The optimum alloy for thick-walled castings is composed of Si = 1.6 wt%, Cu = 0.2 wt%, Ni = 0 wt% and Co = 0 wt%. It offers an enhancement in yield strength and acceptable impact work at low temperatures for massive castings in as cast state. The heat treated, full ferritic material could even improve these results.

A systematic neutron reflectometry study on hydrogen absorption in thin Mg1-xAlx alloy films Special issue on Neutron Scattering in Canada.

In this article, we show how neutron reflectometry (NR) can provide deep insight into the absorption and desorption properties of commercially promising hydrogen storage materials. NR benefits from the large negative scattering length of hydrogen atoms, which changes the reflectivity curve substantially, so that NR can determine not only the total amount of stored hydrogen but also the hydrogen distribution along the film normal, with nanometer resolution. To use NR, the samples must have smooth surfaces, and the film thickness should range between 10 and 200 nm. We performed a systematic study on thin Mg1–xAlx alloy films (x = 0.2, 0.3, 0.4, 0.67) capped with a Pd catalyst layer. Our NR experiments showed that Mg0.7Al0.3 is the optimum alloy composition with the highest amount of stored hydrogen and the lowest desorption temperature. All the thin films expand by about 20% because of hydrogen absorption, and the hydrogen is stored only in the MgAl layer with no hydrogen content in the Pd layer.

Development and Application of High Cr-High Si-Fe-Ni Alloys to High Efficiency Waste-To-Energy Boilers

In order to improve the durability of high efficiency waste-to-energy boilers, it is essential to develop and apply high temperature corrosion-resistant materials having a long life time according to the intensity of the corrosion conditions. Two types of high Cr-high Si-Fe-Ni base and high Cr-high Si-Ni-Fe base alloy seamless tubes; MAC-N (26Cr-3.5Si-11Fe-Ni base) alloy and MAC-F (23Cr-3.8Si-38Ni-Fe base) alloy respectively which contain no expensive Mo and have better corrosion resistance than the existing alloys under severe corrosive environments of waste combustion gas, have developed. The optimum alloy composition range were defermined by confirming the effect of the alloying elements on the corrosion resistance in the laboratory corrosion tests. Furthermore, the seamless tubes were mounted on the actual superheater of the 500oC/9.8MPa high efficiency waste-to-energy boiler to examine the durability over a period of four years. As a result, it was confirmed that the MAC-N and MAC-F alloys have better corrosion resistance than the Alloy625 and 310HCbN. In addition, it has become clear that corrosion resistance of both alloys is displayed through the formation of SiO2 rich protective scale due to the combined addition of the principal elements, Si, Cr, Fe and Ni. Under conditions of high Cl content molten deposits and severe thermal cycle, the corrosion rate increases as the results of deterioration of protective oxidation scale.

Optimization of Mg-Zn-Al-Ca-La Alloys for the Improvement of Casting Properties and Creep Resistance

Mg-0.5%Zn-4%Al-0.5~2.0%Ca-0.5~2.0%La alloys are investigated in order to determine the optimum composition with superior casting properties and excellent creep resistance for automatic transmission case applications. The results show that regardless of the La content, the hot-tearing susceptibility of alloys containing 0.8%Ca or more is low. However, at 0.5%Ca content, hot-tearing occurs in alloys containing more than 1.2%La. The creep resistance of the alloys increases as the Ca content increases and Mg-0.5%Zn-4%Al-0.9%Ca-0.8%La alloy is found to be the optimum alloy exhibiting good casting properties and adequate heat resistance for automatic transmission cases.

Dilute Alloy Designs of 7xxx Aluminum Alloys for Thick Forging Applications

An effort has been made to present optimum alloy designs of commercial 7175 and 7050 type alloys to be used in thick forgings with proper microstructures and properties. The effects of changing alloy constitutions, primarily [Zn+Mg+Cu] and Zn:Mg ratio, on the evolutions of the coarse equilibrium phases and age hardening response are investigated. As a result, equilibrium phases (M,T,S) are evolved depending on alloy constitutions and cooling rate following solutionizing. The formation of the T- and S-phases is effectively controlled in the novel alloys (dilute and with high Zn:Mg ratio). In the slow quench, the redesign promotes homogeneous precipitation of η-phases, leading to higher mechanical properties than conventional alloys. The novel alloys provide microstructural homogeneity and extended heating range, ensuring 7xxx thick forging applications.