Stress Corrosion Cracking Resistance of Cold-Sprayed Al 6061 Deposits Using a Newly Developed Test Fixture

Mala Sharma,Jeremy Schreiber,Victor Champagne,Timothy Eden

doi:10.3390/coatings9070445

Mala Sharma, Jeremy Schreiber + Show 2 more

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https://doi.org/10.3390/coatings9070445

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Abstract

The stress corrosion cracking (SCC) response of Al 6061 bulk deposits produced by high-pressure cold spray (HPCS) was investigated and compared to commercial wrought Al 6061-T6 material. Representative tensile coupons were stressed to 25%, 65% and 85% of their respective yield strength and exposed to ASTM B117 salt fog for 90 days. After exposure, the samples were mechanically tested to failure, and subsequently investigated for stress corrosion cracking via optical and scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS). The results were compared to the wrought Al 6061-T6 properties and correlated with the observed microstructures. Wrought samples showed the initiation of stress corrosion cracking, while the cold-sprayed deposits appeared to be unaffected or affected by general corrosion only. Optical microscopy revealed evidence of stress corrosion cracking in the form of intergranular corrosion in the wrought samples, while no significant corrosion was observed in the cold-sprayed deposits. Fractography revealed wrought samples failed due to multiple mechanisms, with predominant cleavage and intergranular failure, but cold-sprayed samples only failed by ductile dimple rupture. The difference in SCC response between the differently processed materials is attributed to the documented benefits of the cold spray process, which includes maintaining fine grain structure of the feedstock powder and high density after consolidation, low oxidation, and work hardening effect.

Highlights

Efforts to produce highly dense, bulk components with high strength and ductility have shifted focus from traditional metallurgy methods, which have limitations, to the cold spray process [1,2,3,4]
This paper studies the effect of the high-pressure cold spray process on the stress corrosion cracking (SCC) performance of
The stress corrosion cracking response of cold spray deposits was compared to wrought counterparts that were peak-aged

Summary

Introduction

Efforts to produce highly dense, bulk components with high strength and ductility have shifted focus from traditional metallurgy methods, which have limitations, to the cold spray process [1,2,3,4]. The cold spray process involves the acceleration of micron-sized particles in the solid state toward a target, upon which the surface of the powder particle undergoes high levels of plasticity. This plasticity helps to break down surface contaminants on both the powder and substrate (which can be the target or the prior deposited layers of cold spray) leading to a metallic and mechanical bond. Because the material is deposited in the solid state, the microstructure prior to spraying remains relatively intact after spraying, with the exception of some dynamic recrystallization due to high strain levels. Because the process requires high levels of plasticity, it is important to have a feedstock material that can undergo high levels of strain with low energy input, and work-harden sufficiently to obtain

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