Aluminum Cast Alloys Based on the Al–Ce–Si–Mg System: An Influence of Silicon on Crystallization, Phase Composition, and Tensile Properties
Frank Czerwiński, Babak Shalchi Amirkhiz
Abstract
Abstract An attempt at strengthening the aluminum-cerium-based alloys through additions of silicon was assessed using the experimental Al5Ce3Si0.5Mg (wt. pct) cast hypoeutectic composition, designed based on the commercial A356 (Al–7Si–0.3Mg, wt pct) grade by substituting a portion of Si with Ce. To determine a role of Si, the Al5Ce0.5Mg (wt. pct) reference was cast and tested under identical conditions. An addition of 3 wt. pct Si to the Al5Ce0.5Mg base increased the room temperature yield stress almost three times, from 47 to 135 MPa, but reduced its elongation by an order of magnitude from 8 pct to that below 1 pct. A presence of Si led also to essential changes in the alloy crystallization with the melting range widened substantially from 10 °C to 91 °C mainly due to a reduction in the solidus level. As-cast microstructure of the Al5Ce0.5Mg base consisting the primary αAl along with 44 pct of the α Al + Al 11 Ce 3 eutectic was replaced in the Al5Ce3Si0.5Mg alloy with the α Al + AlCeSi 2 coarse lamellae ternary eutectic, bulky compounds having the Ce-rich core of AlCe 2 Si with external shell of Al 2 CeSi 2 along with the quaternary eutectic of fine α Al, Si, Al 2 MgSi/Al 2 Mg 2 Si, and Al–Si–Mg-Ce phases. The fractographic analysis revealed that additions of Si caused a transition from largely ductile fracture to the predominantly brittle mode with crack paths propagating mainly along the interface between the coarse AlCeSi 2 lamellae and Al(Si, Mg) solid solution, which explains the measured drastic reduction in the alloy elongation. Graphical Abstract