Thixoforming : Semi-solid Metal Processing

10.3.5
Thixojoining of Steel
In the following, the process of thixojoining shows the increase in the functionality
and complexity of components by including additional inserts in the semi-solid
matrix during forming. In first investigations, the thixo lateral extrusion process as
described in Section 10.3.3 produced several components (Figure 10.17) with
integrated inserts. Metallographic analyses showed a good connection between the
bulk material and the inserts without any pores at the contact area. Only at the border
area did a change in the grain size indicate a thermal interaction in the form of a heataffected
zone. Further investigations were made to clarify the possibility of joining
lower melting materials such as copper-based alloys.
One of the tool sets utilized for producing thixojoining components with different
insert materials is shown in Figure 10.18a. It consists of an upper and a lower die and
a plunger. These components are made of hot forming tool steel X38CrMoV5-1. The
upper die and the plunger can be moved in the vertical direction by hydraulic
cylinders. The plunger is guided with a sliding bush to reduce the friction in the
narrow gap to the lower die. It also protects the lower die surface against possible
damage. The functional elements (bearing bush and shaft) are just mounted on/in
the plunger.
The materials of the functional elements were varied in the trials. In the case of the
shaft, stainless-steel X5CrNi18-10 and free cutting steel 9SMn28 were used. For the
bearing bush the sinter bronze GBZ12 and copper–beryllium alloy CuCoBe were
tested. The feedstock of cold forming tool steel X210CrW12 (34 mm diameter, 50 mm
height is heated to approximately 1300 C.
Figure 10.17 Joining component produced by thixo lateral
extrusion (a) and metallographic analyses of the contact area
between semi-solid matrix and insert (b).
10.3 Heating and Forming Operationsj389