A Qualitative Study of the Influence of Grooved Mold Surface Topography on the Formation of Surface Marks on As-Cast Ingots of Aluminum Alloy 3003

Prince N Anyalebechi

doi:10.4236/msa.2020.114018

Abstract

The effects of the wavelength and orientation of machined grooves on a mold surface, casting speed, and melt superheat on the formation of surface marks on as-cast ingots were studied with an immersion casting tester and copper mold chill blocks. The mold surface topographies included a polished smooth surface, and those with machined unidirectional parallel contoured grooves oriented either parallel (vertical) or perpendicular (horizontal) to the casting direction. The unidirectional grooves were 0.232 mm deep with wavelength or spacing between 1 and 15 mm. The casting speed and melt superheat were between 1 and 200 mm/s, and 10 and 50 K, respectively. Two primary types of surface marks were observed on ingots cast with the copper mold with smooth surface topography, namely the finer and closely spaced ripples (Type I), and the widely spaced but coarser laps (Type II). The latter were more prevalent at the higher casting speeds and melt superheats. Qualitatively, formation of both types of surface marks on the as-cast ingots of the aluminum alloy 3003 appeared to be alleviated by increase in casting speed and melt superheat, and by the use of molds with grooved surface topography. In fact, casting with a mold surface with 1 mm spaced grooves that are perpendicular to the casting direction eliminated the formation of surface marks at casting speeds greater than 1 mm/s. It also improved the uniformity of the ingot subsurface microstructure and eliminated the associated subsurface segregation.

Highlights

Defective surface marks such as ripples and laps form on as-cast surfaces of aluminum and aluminum alloy ingots and on their continuously cast slabs and bars [1]-[11]
It appears that the observed coarser and more widely spaced lap marks that formed at faster casting speed and higher melt superheat (Figure 3 and Figure 4) are Type II marks instead of Type III marks
The slightly downward bent corners of the surface marks and the fact that they are perpendicular to the casting direction are consistent with the ripple and lap marks that form on commercial-size ingots [1] [2] [3] and continuous cast products [4]

Summary

Introduction

Defective surface marks such as ripples and laps form on as-cast surfaces of aluminum and aluminum alloy ingots and on their continuously cast slabs and bars [1]-[11] These defects and their associated non-uniform subsurface microstructure make it difficult to produce surface-sensitive products such as aluminum foil, beverage can sheets, and aircraft and automotive body sheet from the cast ingots without the expensive scalping operation [12]. This is despite improvement in ingot casting technology such as the development of electromagnetic casting and low head composite mold casting processes. This extra process step costs the aluminum industry more than ten million dollars a year and reduces recovery

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Conclusion