1) Test pieces 4 mm x 3 mm x 40 mm

2) Calculated values

3) Depending on heat treatment condition

^* Calculated values

In the molten state Si and Al are mutually soluble, whereas in the rapidly solidified condition there is minimal solubility of Si in Al (< 0.3%) and even less solubility of Al in Si. The products are true alloys rather than metal-matrix composites (such as AlSiC) as all the phases present originate from an homogeneous melt.

The Al phase is continuous up to ~ 85%Al. Over approximately 40% Si, the Si phase also becomes continuous, offering a co-continuous duplex alloy (similar to AlBe alloys).

The continuous Si phase produces a stiff alloy with low thermal expansion and low internal stresses, whereas the continuous Al phase enhances thermal conductivity and toughness and lowers electrical resistance.

Consequently, as the Al content is increased, electrical conductivity, thermal conductivity, strength, toughness, CTE and machinability are also increased. For these reasons, it is best to choose the highest Al content alloy that is acceptable for the application.

Although Sandvik can supply machined components with Si contents as high as 85% Si (i.e. CE5), the relative brittleness of this composition means whenever feasible it is often better to compromise on the exact expansion match required and use a lower Si content alloy. For example, Kovar^* packages (with a CTE of ~ 7ppm/°C) have been successfully replaced with CE9, CE11 and even CE13.

^* Kovar is a trademark of Carpenter Technology Corporation