Abstract
The paper presents the results of investigation of the influence of AlFeP and AlSr modifiers on the structure of the hypereutectoid silumin, AlSi21CuNi. The silumin has been modified in two stages. The first stage was melt with the addition of phosphor in the quantity of 120ppm. The second stage was combined application of phosphor and strontium. The strontium addition amounted 150, 250 and 350 ppm. At each melt, the metal has been cast after 10, 30, and 60 minutes from the introduction of the modifiers. The effectiveness of the modification has been assessed basing on qualitative and quantitative analysis of the microstructure of castings. It has been determined that the applied addition of phosphor causes significant comminution of the primary silicon secretions. Maximum comminution of primary silicon has been obtained after the longest time of the modified alloy soaking. The most advantageous effects of combined modification have been obtained with the application of 120ppm addition of P and 350ppm addition of Sr after 60 minutes from the introduction of the modifiers to the metal bath.
Highlights
The AlSi21CuNi alloy belongs to the group of piston hypereutectoid silumins
The mechanism of phosphor acting in modification of hypereutectoid silumins is different from that of strontium acting in the process of eutectic mixture modification in hypoeutectic alloys
The analyses presented above show that, with extension of the modified alloy soaking time, the degree of comminution of the primary silicon secretions increases, but the effect of eutectic mixture refinement gets weaker
Summary
The AlSi21CuNi alloy belongs to the group of piston hypereutectoid silumins. The structure of the alloy consists of hard primary secretions of phase â (Si) and relatively soft eutectic mixture (á +â) and intermetallic phases. The structure of the obtained castings consists of significantly comminuted (down to the sizes below 50 μm) primary silicon secretions with compact wall structure, evenly distributed in the matrix of the irregular lamellar eutectic mixture (α +β) [3]. A survey of literature [6,7,8] shows that, in the case of hypereutectoid silumins, there is a possibility of further structure improvement and, obtaining better mechanical properties of the castings This is to be achieved due to the change of the morphology of the irregular lamellar eutectic mixture into one with fibrous structure while maintaining the adequate degree of comminution and even distribution of the primary silicon secretions. The use of those techniques, is complicated and, limited
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