Effect of Silicon content and solutionizing temperature on the Mechanical Properties in a Sand Molded Aluminum 206 (Al Cu4) Casting

F. Chiesa*, D. Levasseur, Jeremy Carignan

Centre de métallurgie du Québec, Trois-Rivières, Québec

REGAL Aluminium Research Center

B. Duchesne

Collège de Trois-Rivières, Trois-Rivières, Québec

(*Corresponding author; )

ABSTRACT

Aluminium A206 (AlCu4) is one of the strongest aluminium casting alloy with tensile properties approaching those of ductile iron. If the specification on the silicon content (< 0.05%) is easy to achieve during alloy ingot production, it is not the case in a foundry, where returns are used which are not perfectly cleaned from the silicate molding sand. In A206, the Si content is controlled in order to avoid the formation of low melting point intermetallic phases (such as phase Q Al5Cu2Si6Mg2); these phases will melt during the solutionizing heat treatments to which alloy A206 must be subjected to develop its outstanding mechanical properties. This incipient melting may deteriorate the mechanical properties of Alloy A206 if the solutionizing treatment is applied at the standard temperature of 530°C.

In the present study, a lower temperature solutionizing (520°C) was applied to reduce or eliminate incipient melting of the silicon containing Q phase. This was carried out on a complex shape industrial casting weighing 14 kg (31lbs) and 560x410x250mm (22x16x10”) in size poured in aluminum 206 with a high silicon content (0.22% vs 0.05% max for alloy A206). Twenty ASTM E7 subsize tensile specimens were excised from two locations in the casting iin order to compare the tensile properties for the two solutionizing temperature. Optical and SEM microscopy allowed to investigate the causes of the differences in the properties observed between the 2 zones of the casting studied for 3 different heat treatments.

Keywords: Aluminum-copper alloys, sand casting, tensile properties, heat treatment, Solidification modeling

Figure 1 - Location of 10 tensile samples blanks inside the 560x410x250mm, 14kg aluminum 206 casting