Microstructure studies were conducted on metallographic samples worked according
to standard ASTM E3-11 [7].
Microscopic investigation was performed using Neophot-21 light microscopy
equipment. Quantitative evaluation of structural components amount has been carried
out in accordance with GOST 5639 [8] requirements, followed by computer calculating
of experimental microstructural images data using software Adobe Photoshop.
Scanning electron microscopy investigation and X-ray spectral microscopic
analysis were carried out on equipment Superprobe-733 (JEOL, Japan). Resolution of
electron microscope according to Passport: 7nm. To study the structural condition of
specimens (at accelerating voltage 25 kV) surfaces at different scales in secondary
electrons mode (SEI) have been scanned. Researches of chemical heterogeneity and
elements distribution have been done in X-ray radiation AlKα, FeKα, CuLα, ZnLα,
and also in back reflected electrons (COMPO).
Mechanical tension tests were performed according to GOST 1497 [9] on the
INSTRON testing machine. The impact toughness test was conducted in accordance
with GOST 9454 [10] on PSW-5 swing equipment.
2. Phase composition and structure of industrial bronze BrA9Zh3L. Among
all tin-free foundry bronzes per GOST 493 [4] BrA9Zh3L is one of the most popular
commercial industrial electrotechnical products with high structural properties and
with the best combination of strength and plasticity indexes [11].
The main components of this alloy are copper, aluminum and iron.
Cu-Al. Area of copper-based solid solutions (α-phase), according to binary
copper-aluminum diagram [12-15], extends to 9,4 wt. % Al. With temperature
lowering, solubility of aluminum in copper rises and at temperatures 1037, 900, 800,
700, 500°C becomes 7,4; 7,8; 8,2; 8,8; 9,4 wt. % Al, respectively. The α-phase has an
FCC similar to pure copper lattice, period of which increases up to 0,3565nm at 10.5
wt. % Al content in alloy.
β -phase is a solid solution based on compound Cu
3
Al (12,44 wt. %Al). In alloys
of the β region, depending on heat treatment conditions [16], two metastable
intermediate phases can be observed.
γ
1
-phase is a solid solution based on compound Cu
3
Al
4
. It exists in the range of
concentrations 16.0 ... 18.8 wt. % Al and has monoclinic lattice with 102 atoms in its
elementary cell. Phase γ
2
has a lattice similar to α-phase lattice.
In area up to 20% Al alloy’s liquidus consists of the phases’ α, β, χ, and χ
1
four
branches of primary crystallization. Eutectic α + β with eutectic point at 8.5% Al is
crystallized at 1037°C. Peritectic reactions L + β ↔ χ and L + χ ↔ γ1 occur at
temperatures 1036 and 1022°C, respectively. χ -phase exists in 1036 ... 936°C
temperature range. β -phase crystallizes from the melt according to curve with
maximum at 1048°C and an appropriate concentration of 12.4 wt. %Al. In solid state
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