In connection with the chemical composition the conditions of the thermal treatment influence 
the transformation behaviour and consequently the formation of the microstructure of the 
alloys. By application of low cooling rates the equilibrium conditions are valid approximately 
and it is possible to describe the transformation behaviour by the application of the phase 
diagrams ( Fig. 1). In this report the complex aluminium bronzes with higher aluminium 
contents ( from about 10 mass - % to 16 mass - % ) are interesting. The disordered bee ß — 
phase crystallizes from the melt and the precipitation of the k — phase from the  — phase is 
observed as shown in Fig. 1d. During the slow cooling of hypoeutectoid alloys the B — phase 
transforms into the proeutectoid fcc a — phase and the eutectoid (a + v2 ). 
Met 5B ->pP+tko>B+tkta>(at+ty)tkta 
At the hypereutectoid alloys the proeutectoid formation of the y, — phase takes place instead 
of the proeutectoid formation of the a. — phase: 
Melt >Bß >B+Kk—>ßB+k+y2—>(at+yı)+k+y2 
Under practical processing conditions the cooling rate is higher and the diffusion controlled 
phase transformations are retarded or suppressed. Bainitic and martensitic phase 
transformations or a stabilization of the ß — phase in dependence from the chemical 
composition and the cooling conditions are observed / 6 /. A corresponding transformation 
diagram of binary alloys is presented in Fig. 2 / 7 /. The full lines mark the phase diagram, the 
broken lines mark the transformation temperatures of the martensitic transformations ( Ms ) 
and of the ordering transformations ( T. ) of the high temperature phase ß. It is to see, that 
three martensitic phases named with a’, 3,” and vy,” appear in dependence of the aluminium 
content. Higher aluminium contents and additional alloying elements stabilize the ß — phase 
which transforms by two ordering transformations during the cooling. 
disordered bee B — ordered bee Ba — ordered orthorhombic 3; 
The autors / 7 / remark that it is not possible to suppress these ordering transformations of the 
B — phase in binary alloys by a quenching from the f§ — region. 
Small specimens of the alloys were applied to the heat treatments, which consist in a 
tempering in the PB - region and oil quenching ( betatization ). By quenching of the specimens 
in cold water intergranular cracks can be produced in the microstructure. The annealing 
experiments were carried out at temperatures from 500°C to 700°C, detention time 30 minutes 
and air cooling. 
The specimens were metallographically prepared by mechanical grinding and polishing. An 
etchant consisting of 10g ammonium persulfate + 100 ml aqua dest. was applied to the 
specimens. 
The X — Ray diffraction by use of Cu — Ka - radiation was carried out to identify the phases 
in the microstructure. 
3. Results and Discussion 
3.1 Characterization of the microstructure of the base alloys 
Fig. 3 shows the microstructure of the sand cast alloy. In the coarse - grained microstructure 
three phases are observed: the intermetallic compound vy; ( Cuy Aly ), which appears in form 
of seams at the former B — grainboundaries and in form of particles inside of the former 3 — 
grains, the B; — phase ( Cu; Al) and small precipitations of the k — phase. The y, — phase has a 
complex cubic structure and shows a brittle behaviour similar to the y — phase in brasses / 6 /. 
The B; — phase has an ordered orthorhombic structure / 6, 7 /. The x — precipitations have a Cs 
Cl — type structure / 6 /. In the X — ray diffraction pattern of the cast alloy the reflections of 
41