Abstract
This work analyzes the effect of Cu additions on the microstructure of quaternary alloys Al-6Si-7Mg-xCu (x= 3, 5 and 7 wt.%) produced by conventional metallurgy. Microstructural modifications were studied using Optical Microscopy (OM), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), focusing on second phases identification and quantification. Conventional image analyses were developed measuring the total percentage of second phases, and individually for each phase determining its equivalent diameter, shape factor, roundness and aspect ratio; while fractal analyses were carried out complementarily through fractal dimension measurements for the whole microstructure and for individual phases. Compression tests were also carried out. SEM and XRD results revealed that second phases were eutectic Si, Mg2Si, Al2Cu and Al5Cu2Mg8Si6 (Q). The increase in Cu content led to higher quantities of these phases, mainly Al2Cu, which was barely present for the alloy with the lowest Cu content. Morphologies of second phases depended on Cu content, being present as eutectic, block like, finely dispersed or primary particles. The combination of conventional and fractal parameters provided a useful tool for comparatively analyze microstructural modifications and second phases features. It was also found that the compressive behavior of the alloys depended on the resulting microstructures.
Highlights
Research focused on aluminum alloys has been developed in an uninterrupted way in the last years, been published many works mainly related to microstructural modifications, which derivate from the presence of different second phases with a wide variety of morphologies, i.e. block-like, fibrillar, particulate, acicular, Chinese script, etc[1,2,3,4]
For the alloy with 5% of Cu (Cu5) microstructure is quite different from the alloy Cu3, predominating block-like Cu-rich phases of sizes significantly higher. For this alloy the content of Al2Cu significantly increased, while Mg2Si presents a morphology different compared to Figure 1a because it is markedly irregular and seems to be isolated parts of agglomerates similar to Chinese scripts[5]
The increase in Cu content for alloys Cu5 and Cu7 favored the formation of Al2Cu due to the availability of this element in the molten liquid, not enough in the alloy with 3% Cu, just precipitating Q phase from liquid
Summary
Research focused on aluminum alloys has been developed in an uninterrupted way in the last years, been published many works mainly related to microstructural modifications, which derivate from the presence of different second phases with a wide variety of morphologies, i.e. block-like, fibrillar, particulate, acicular, Chinese script, etc[1,2,3,4] The presence of these phases in Al alloys directly depends on alloying elements content and manufacturing process, affecting their final mechanical properties. In search of significant microstructural modifications, previous works have studied Mg contents between 3 and 11%5,8 This element led to the formation of metallic foams are generally manufactured using methods such as infiltration of liquid metal, powder metallurgy and liquid processes[9,10,11], a solid-state method has Materials Research been previously reported for Al alloys, generating connected or non-connected pores, depending on the alloy system[5,12]. It is used since it is common to analyze particles as if they were spheres
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