The subject of this invention is hypo-eutectic silumin with additive of wolfram and vanadium designed for pressure die casting.

Hypo-eutectic silumin alloys, mostly used for pressure die casting, contain following chemical elements in weight percentage: 8,0-11,0% Si; 0,60-1,3% Fe; 2,0- 4,0% Cu; 0,10-0,55% Mn; 0,05-0,55% Mg; 0,00-0,15 % Cr; 0,30-0,55 % Ni; ~1,2 % Zn; 0,15-0,25 % Ti.

Silumin of composition indicated above is characterized by a microstructure consists of: solid solution of alloy addition in aluminium (α) and complex eutectic mixture. Eutectic mixture composition may also include, besides phase α, solid solution of alloy addition in silicon (β) and intermetallic phases: Al₂Cu, Al₉Fe₃Si₂, Mg₂Si and AlSiCuFeMnMgNiCrSnTi.

Mechanical properties of described pressure die casting silumin are following: tensile strength R_m ≥ 240 MPa; yield strength R_p0,2 ≥ 140 MPa; unit elongation A < 1 %, hardness HBW ≥ 80. Development of silumin with thickness comparable to the alloy described above and higher strength properties, enables getting pressure castings with lower wall thickness and the same strength parameters.

Silumin which includes W and V, in accordance with the invention contains in weight percentage: 7,5-8,7%, Si; 0,7-1,2% Fe; 2,0- 3,0% Cu; 0,10-0,50% Mn; 0,05-0,50% Mg; 0,00-0,15 % Cr; 0,05-0,40 % Ni; 0,9-1,1 % Zn; 0,00-0,10 % Ti; 0,10-0,30 % W and 0,10-0,30 % V.

Into hypo-eutectic silumin, wolfram and vanadium were introduced in the form of master alloy AlW8 and AlV10. Application of master alloys allows dissolution of W and V in silumin. Both wolfram and vanadium does not dissolve, in solid state aluminium, however they form with aluminium many varieties of intermetallic phases. Release of significant quantity of intermetallic phases in silumin, especially in the form of releases of relatively big sizes and complex morphology, results in increasing brittleness and decreasing its tensile strength R_m. Silumin crystallization process inside pressure casting die arises very intensively, which causes the possibility of supersaturation with wolfram and vanadium phase α. Phase α supersaturated with wolfram and vanadium may be characterized by higher mechanical properties in relation to solid solution α present in hypo-eutectic silumin without additive of W and V. Introduction of W and V additive into hypo-eutectic silumin for pressure die casting allows to obtain alloy with better mechanical properties in relation to commonly used in the range of this technology hypo-eutectic silumin alloys. Condition of obtaining hypo-eutectic silumin with additive of W and V of increased mechanical properties is supersaturation of solid solution α with wolfram and vanadium and avoidance of intermetallic phases release of relatively big sizes and complex morphology from equilibrium systems Al-W and Al-V.

Pressure casting made from silumin in accordance with the invention presents high tensile strength R_m and high unit elongation A.

The subject of the invention is illustrated with the example below, with reference to the fig. 1 a-c, where microstructure of examined silumin alloys is presented.

Initial silumin was melted in the melting furnace heated with gas, with maximum charge capacity of 1,5 tons. The chemical composition of silumin was following: % in weight Si Fe Cu Mn Mg Cr Ni Zn Ti Al 8,66 0,86 2,36 0,23 0,33 0,04 0,11 0,93 0,05 rest

After melting silumin was refined inside the furnace. Ecosal Al - 113S was used for refining in the amount of ca. 0,25 kg per 500 kg bath content. After tapping silumin from the furnace to the ladle of 300 kg Al alloy capacity, it was slagged with slag trap Ecremal N44. Into 300 kg of silumin poured off to the ladle, 1 (one) hand shank ZUDX-5501 0,20 kg of slag trap was added. After slagging silumin was transported to heating resistant furnace at the cold-chamber pressure die-casting machine with horizontal stamping chamber - Idra OL700S. Inside heating furnace composition of silumin was completed with master alloys containing vanadium and wolfram, and these were accordingly AlV10 and AlW8. Temperature of silumin inside heating furnace was 750 °C. In this temperature the alloy with master alloys was kept for 20 minutes. During this time period master alloy AlV10 and AlW8 were totally dissolved. Pressure castings were produced from 3 (three) silumin variants with additive of W and V. The amount of initial silumin and master alloys AlV10 and AlW8 was taken in such manner so the following chemical composition of three silumin variants with additive of W and V was obtained: Silumin % in weight variant Si Fe Cu Mn Mg Cr Ni Zn Ti W V Al 1 8,66 0,81 2,52 ; 0,20 0,35 0,04 0,12 0,95 0,04 0,10 0,10 rest 2 8,40 0,87 2,32 0,22 0,33 0,03 0,11 0,91 0,04 0,20 0,20 rest 3 7,99 0,85 2,37 0,21 0,33 0,03 0,10 0,90 0,04 0,30 0,30 rest

The most of produced pressure casting were characterized by 2 mm wall thickness. From these castings samples for tensile strength testing were taken. These were flat samples with rectangular section dim. 2 mm / 10 mm. Tensile test was performed on testing machine

Instron 3382. Applied tension velocity was 1 mm/min. During this test following factors were determined: tensile strength R_m, yield strength R_p0,2 and unit elongation A. Hardness was determined by Brinell method. For silumin alloys with additive of W and V the following values of mechanical properties were achieved: Silumin Mechanical properties variant R_m, MPa R_p0,2, MPa A, % HB 1 275 119 4,4 114 2 299 119 6,3 114 3 299 117 5,7 113

The microstructure of silumin with additive of W and V is presented on fig. 1 (a-c). It is composed of solid solution of alloy addition in aluminium (α), ternary eutectic α+Al₉Fe₃Si₂+β and quaternary eutectic α+Al₂Cu+AlSiCuFeMgMnNiVW+β.