Service performance of engineering materials

Corrosion research by Atrens and co-workers has made significant contributions to the understanding of the service performance of engineering materials. This includes: (1) elucidated corrosion mechanisms of Mg alloys, stainless steels and Cu alloys, (2) developed an improved understanding of passivity in stainless steels and binary alloys such as Fe-Cr, Ni-Cr, Co-Cr, Fe-Ti, and Fe-Si, (3) developed an improved understanding of the melt spinning of Cu alloys, and (4) elucidated mechanisms of environment assisted fracture (EAF) of steels and Zr alloys. This paper summarises contributions in the following: (1) intergranular stress corrosion cracking of pipeline steels, (2) atmospheric corrosion and patination of Cu, (3) corrosion of Mg alloys, and (4) transgranular stress corrosion cracking of rock bolts.

The effect of aluminium content on the mechanical properties and microstructure of die cast binary magnesium-aluminium alloys

This paper investigates the relationship between mechanical properties and microstructure in high pressure die cast binary Mg-Al alloys. As-cast test bars produced using high pressure die casting have been tested in tension in order to determine the properties for castings produced using this technique. It has been shown that increasing aluminium levels results in increases in yield strength and a decrease in ductility for these alloys. Higher aluminium levels also result in a decrease in creep rate at 150 degrees C. It has also been shown that an increase in aluminium levels results in an increase in the volume fraction of eutectic Mg17Al12 in the microstructure.

The effect of silicon content on the microstructure and creep behavior in die-cast magnesium AS alloys

The effect of increasing levels of silicon on the microstructure and creep properties of high-pressure die-cast Mg-Al-Si (AS) alloys has been investigated. The morphology of the Mg2Si phase in die-cast AS alloys was found to be a function of the silicon content. The Mg2Si particles in castings with up to 1.14 wt pct Si have a Chinese script morphology. For AS21 alloys with silicon contents greater than 1.4 wt pet Si (greater than the alpha-Mg2Si binary eutectic point), some Mg2Si particles have a coarse blocky shape. Increasing the silicon content above the eutectic level results in an increase in the number of coarse faceted Mg2Si particles in the microstructure. Creep rates at 100 hours were found to decrease with increasing silicon content in AS-type alloys. The decrease in creep rate was most dramatic for silicon contents up to 1.1 wt pct. Further additions of silicon of up to 2.64 wt pct also resulted in significant decreases in creep rate.

Iron-rich intermetallic phases and their role in casting defect formation in hypoeutectic Al-Si alloys

Iron is the most common and detrimental impurity in aluminum casting alloys and has long been associated with an increase in casting defects. While the negative effects of iron are clear, the mechanism involved is not fully understood. It is generally believed to be associated with the formation of Fe-rich intermetallic phases. Many factors, including alloy composition, melt superheating, Sr modification, cooling, rate, and oxide bifilms, could play a role. In the present investigation, the interactions between iron and each individual element commonly present in aluminum casting alloys, were investigated using a combination of thermal analysis and interrupted quenching tests. The Fe-rich intermetallic phases were characterized using optical microscope, scanning electron microscope, and electron probe microanalysis (EPMA), and the results were compared with the predictions by Thermocalc. It was found that increasing the iron content changes the precipitation sequence of the beta phase, leading to the precipitation of coarse binary beta platelets at a higher temperature. In contrast, manganese, silicon, and strontium appear to suppress the coarse binary beta platelets, and Mn further promotes the formation of a more compact and less harmful a phase. They are therefore expected to reduce the negative effects of the phase. While reported in the literature, no effect of P on the amount of beta platelets was observed. Finally, attempts are made to correlate the Fe-rich intermetallic phases to the formation of casting defects. The role of the beta phase as a nucleation site for eutectic Si and the role of the oxide bifilms and AIP as a heterogeneous substrate of Fe intermetallics are also discussed.