Purpose – The purpose of this paper is to quantify the corrosion damage evolution that has occurred on the aircraft aluminum alloy 2024 after the exposure to Exfoliation Corrosion Test (EXCO) solution. Moreover, the effect of the evolving corrosion damage on the materials mechanical properties has been assessed. The relevance of the corrosion damage induced by the exposure to the laboratory EXCO for linking it to the damage developed after the exposure of the material on several outdoor corrosive environments or in service is discussed. Design/methodology/approach – To induce corrosion damage the EXCO has been used. For the quantification of corrosion damage the metallographic features considered have been pit depth, diameter, pitting density and pit shape. The effect of the evolving corrosion damage on the materials mechanical properties has been assessed by means of tensile tests on pre corroded specimens. Findings – The results have shown that corrosion damage starts from pitting and evolves to exfoliation, after the development of intergranular corrosion. This evolution is expressed by the increase of the depth of attack, as well as through the significant growth of the diameter of the damaged areas. The results of the tensile tests performed on pre corroded material made an appreciable decrease of the materials tensile properties evident. The decrease of the tensile ductility may become dramatic and increases on severity with increasing corrosion exposure time. SEM fractography revealed a quasi-cleavage zone beneath the depth of corrosion attack. Originality/value – The results underline the impact of corrosion damage on the mechanical behavior of the aluminum alloy 2024 T3 and demonstrate the need for further investigation of the corrosion effect on the structural integrity of the material. This work provides an experimental database concerning the quantification of corrosion damage evolution and the loss of material properties due to corrosion.

No abstract

A B S T R A C TThe mechanical behaviour of two hot rolled magnesium alloys, namely the AZ31 and AZ61, has been evaluated experimentally under both monotonic and cyclic loading. Both longitudinal (L) and long transverse (LT) directions were evaluated. The tensile behaviour of the L and LT directions is similar and differs only in the offset 0.2% yield strength for both materials. This difference is attributed to the angular spread of basal poles toward the rolling direction and is more pronounced for the case of AZ31. A distinct hardening response is obvious in both directions. Twinning formation was observed; it is more pronounced in the longitudinal direction while the fracture mode is intergranular and equiaxed facets are present in the fracture surfaces of the specimens. The S-N curves exhibit a smooth transition from the low to high cycle fatigue regime. AZ61 exhibits an overall better fatigue behaviour compared to AZ31. A transgranular crack initiation mode is observed in all tested specimens while the propagation of the cracks is characterized as intergranular.A f = elongation to failure (%) f = frequency (Hz) HV = hardness vickers (MPa) K(t) = stress concentration factor (−) N f = cycles to failure (−) P 1 , P 2 , P 3 , P 4 = regression analysis coefficients R = stress ratio (−) R m = ultimate tensile strength (MPa) R p0.2 = offset yield strength (MPa) W = strain energy density (MJ/m 3 ) σ f = fatigue limit (MPa) σ max = maximum applied stress (MPa) I N T R O D U C T I O NMagnesium is the lightest structural engineering metal, and therefore, particularly attractive for structural applications where weight saving is of major importance. Improvements in mechanical properties, corrosion resistance 1,2 and the development of advanced manufacturing processes have led to increased interest in magnesium alloys and several works are in progress to develop wrought magnesium alloys for automotive and aerospace applications. 3-5 Amongst them, AZ31 and AZ61 represent two of the most popular wrought alloys of the AZ family for light-weight structures; diverse uses include satellite components, military applications, door inner automotive components, computer cases, cameras, 6 etc. The major problems limiting the use of wrought magnesium alloys in aircraft structure applications are the high corrosion susceptibility and the poor damage tolerance behaviour. Although the corrosion problem can be presently faced by means of proper coating technologies, 7 the fatigue issue 812

The potential of cast magnesium alloys for being used as structural materials in lightweight applications is assessed. The ability of the alloys for mechanical performance is evaluated and compared against the ability of widely used structural aircraft cast aluminum alloys. The specific quality index QDS, devised for evaluating both cast and wrought aluminum alloys, will be exploited to evaluate the ability of a number of cast magnesium alloys for mechanical performance. The exploited quality index QDS involves the material’s yield strength Rp to account for strength, the strain energy density W to account for both tensile ductility and toughness, and the material’s density ρ. The effects of differences in chemical composition and heat treatment conditions on the mechanical performance of cast magnesium alloys have been assessed. The use of the quality index QDS has been proved to appreciably facilitate the evaluation of the mechanical performance of cast magnesium alloys and also the comparison between alloys of different base materials. The results quantify the gap to be closed such as to involve cast magnesium alloys in aircraft structural applications.

No abstract

No abstract

No abstract

A B S T R A C T In the present work, an investigation on the high stress sensitivity of the fatigue life of the AZ31 rolled magnesium alloy under constant amplitude fatigue loading has been carried out. Different damage parameters were involved to quantify fatigue damage accumulation at the various scales of material volume corresponding to the changing fatigue damage mechanisms that prevail at the various stages of the fatigue life. The experimental work included mainly nano-indentation measurements to evaluate hardness evolution at the nano-scale due to cyclic plasticity, results of micro-crack monitoring by using the replication technique and fractographic analysis to obtain the fracture characteristics of the fatigue specimens after failure. The hexagonal close-packed structure of the alloy and the resulting difficulty for the activation of five independent slip systems required for homogeneous plastic deformation were considered to determine the high stress sensitivity of the fatigue life observed for the rolled AZ31 alloy under the investigated loading conditions. A f = elongation to failure [%] E = Young's modulus [GPa] f = frequency [Hz] H = mean nano-hardness [GPa] K(t) = stress concentration factor [-] N f = cycles to failure [-] P = maximum load for nano-indentation test [μN] R = stress ratio [-] R m = ultimate tensile strength [MPa] R p0.2 = offset yield strength [MPa] W = strain energy density [MJ/m 3 ] σ max = maximum applied stress [MPa] σ f = fatigue limit [MPa]