Microstructure and Indentation Properties of Single-Roll and Twin-Roll Casting of a Quasicrystal-Forming Al-Mn-Cu-Be Alloy

Abstract

In this investigation, strips of an experimental Al-Mn-Cu-Be alloy were manufactured by high-speed single-roll and twin-roll casting to stimulate the formation of a quasicrystalline phase during solidification. The strips were characterised by light microscopy, scanning and transmission electron microscopy, microchemical analysis, and X-ray diffraction. Indentation testing was used to determine the mechanical responses of the strips in different areas. A smooth surface was achieved on both sides of the twin-roll-cast strip, while the free surface of the single-roll-cast strip was rough. The microstructures in both strips consisted of an Al-rich solid solution matrix embedding several intermetallic phases Θ-Al2Cu, Be4Al (Mn, Cu), Al15Mn3Be2 and icosahedral quasicrystalline phase (IQC). The microstructure of the single-roll-cast strip was more uniform than that of the twin-roll-cast strip. Coarse Al15Mn3Be2 particles appeared in both alloys, especially at the centre of the twin-roll strip. These coarse particles adversely affected the strength and ductility. Nevertheless, both casting methods provided high-cooling rates, enabling the formation of metastable phases, such as quasicrystals. However, improvements in alloy composition and casting procedure are required to obtain enhanced microstructures and properties.

Microstructure and Properties after Friction Stir Processing of Twin-Roll Cast Al–Mn–Cu–Be Alloy

“…The compo-sition of the alloy is presented in Table 1. More details regarding the casting processes are given in [9]. Afterwards, the strips were treated by FSP using a universal milling machine Prvomajska ALG 200, Zagreb, Croatia.…”

“…The initial as-cast microstructure was not uniform and could be seen on both sides of the processed zone. Since it was investigated in detail in our previous paper [9], only basic information is given here. At the roll side, a thin outer equiaxed zone formed (E in Figure 2), which was followed by elongated grains (region M, thickness around 900 µm) with the size 238 ± 80 µm × 63 ± 27 µm.…”

“…The casting speed of bands (3-5 mm thick, 100 mm wide) can be up to 60 m/min [8]. However, they have a non-uniform as-cast microstructure [9].…”

“…The initial material for the study was an Al-Mn-Cu-Be alloy produced by twin-roll casting [9]. It has a non-uniform microstructure, possessing coarse intermetallic particles throughout the strip, especially at its centre.…”