Thixoforming : Semi-solid Metal Processing

106j 4 Design of Al and Al–Li Alloys for Thixoforming
Figure 4.1 Alternative thixoforming processes [1].
Chemical grain refinement is a process that offers lower processing costs and is
from an economic point of view considered as an alternative to the other processes
mentioned above [5]. The fine grain structure is achieved with the aid of alloying
elements (e.g. AlTi5B1) that act as heterogeneous nucleating agents [5]. The grain
refiners are in the form of a wire injected directly into the melt. Other elements can
also be added to enhance the grain refining properties of these elements (so-called
modification) [4]. It was furthermore verified that the chemical grain refinement of
aluminium alloys has an advantageous effect on the castability and other technologically
important properties. The further targeted development of an A356–
AlSi7Mg0,3 alloy by means of grain refinement and modification using Ti and Sr
was investigated in 2003 [6]. One possibility for further refinement of the grain
structure is the combination of chemical refinement with the MHD process [7].
The raw material has to be reheated precisely to a target temperature in the
solidus–liquidus range [8]. Rapid heating prevents undesired grain growth and
makes higher cycling rates possible. In this respect, inductive heating offers