Abstract
Porosity in aluminum alloys is a great concern to the casting and automotive industry. In this publication, porosity formation in air-melted and vacuum induction melted (VIM) aluminum alloys was studied and compared to understand its effect on microstructure and mechanical properties of Al-7Si alloys. Al-7Si alloys were cast at 700°C and 900°C in a muffle furnace and VIM furnace. Microstructural results show that the alloys cast in muffle furnace refined the eutectic silicon compared with the cast samples prepared in VIM furnace. X-ray computed tomography (XCT) was used for three-dimensional (3D) visualization and quantification of porosity in these alloys. The volume fraction of pores was observed to be higher in alloy air-melted at 900°C compared with 700°C. XCT results from VIM alloy samples showed no significant porosity when cast at either 700°C or 900°C. The morphology of large pores in alloys air-melted at 700°C represents the formation of shrinkage porosity due to the incomplete flow of molten metal during solidification. Tensile test results show that the elongation property of VIM alloy was increased by more than 20% compared with air-melted alloy. The tensile strength and elongation were observed to be higher for alloy samples cast at 700°C compared with 900°C for both air-melted and VIM alloys. The findings from microstructure, XCT, and tensile tests show that vacuum induction melting improves the mechanical properties of the alloy compared with air-melted alloy.
Highlights
Porosity formation in cast aluminum alloys is a significant concern as it deteriorates the mechanical properties.[4]
Melt treatment of aluminum alloys plays an important role in aluminum castings
Melt superheating is an industrially viable melt treatment method in aluminum castings due to its ease of application compared with other methods
Summary
Aluminum-silicon alloys are widely used in automotive, aerospace, communication, and domestic casting applications due to their high strength to weight ratio, high thermal conductivity, high formability, and corrosion resistance.[1,2,3] porosity formation in cast aluminum alloys is a significant concern as it deteriorates the mechanical properties.[4]. Treatment), physical and mechanical treatments (using vacuum, ultrasonic vibration, electromagnetic fields, stirring, etc.), and chemical methods (addition of modifiers or grain refiners to the melt).[6] Among these methods, melt superheating is an industrially viable melt treatment method in aluminum castings due to its ease of application compared with other methods. VIM is viable industrially because of its independent control of time, temperature, pressure, and mass transport by melt stirring.[15] VIM offers several advantages such as ease of operation, low oxidation losses, precise control of temperature, low level of environmental pollution from dust output, removal of impurity elements with high vapor pressures on recycling scrap, removal of dissolved gases, etc.[15] Nowadays, vacuum-assisted castings are gaining importance in the casting and automotive industries because of their ability to decrease porosity formation and improve mechanical properties.[16,17,18] it is essential to compare the porosity formation and its effect on the mechanical properties of Al–Si alloys prepared by the vacuum induction melting versus air melting method. 3D xray tomography to visualize and quantify porosity in air-melted and VIM cast Al-7Si alloys is presented and discussed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
