Heat treatment of a casting elements poured from silumins belongs to technological processes aimed mainly at change of their mechanical properties in solid state, inducing predetermined structural changes, which are based on precipitation processes (structural strengthening of the material), being a derivative of temperature and duration of solutioning and ageing operations. The subject-matter of this paper is the issue concerning implementation of a heat treatment process, basing on selection of dispersion hardening parameters to assure improvement of technological quality in terms of mechanical properties of a clamping element of energy network suspension, poured from hypoeutectic silumin of the LM25 brand; performed on the basis of experimental research program with use of the ATD method, serving to determination of temperature range of solutioning and ageing treatments. The heat treatment performed in laboratory conditions on a component of energy network suspension has enabled increase of the tensile strength Rm and the hardness HB with about 60-70% comparing to the casting without the heat treatment, when the casting was solutioned at temperature 520 o C for 1 hour and aged at temperature 165 o C during 3 hours.
Tests concerning EN AC 48000 (AlSi12CuNiMg) alloy phase transition covered (ATD) thermal analysis and (DSC) differential scanning calorimetry specifying characteristic temperatures and enthalpy of transformations. ATD thermal analysis shows that during cooling there exist: pre-eutectic crystallization effect of Al9Fe2Si phase, double eutectic and crystallization α(Al)+β(Si) and multi-component eutectic crystallization. During heating, DSC curve showed endothermic effect connected with melting of the eutectic α(Al)+β(Si) and phases: Al2Cu, Al3Ni, Mg2Si and Al9Fe2Si being its components. The enthalpy of this transformation constitutes approx. +392 J g-1 . During freezing of the alloy, DSC curve showed two exothermal reactions. One is most likely connected with crystallization of Al9Fe2Si phase and the second one comes from freezing of the eutectic α(Al)+β(Si). The enthalpy of this transformation constitutes approx. –340 J g-1 . Calorimetric test was accompanied by structural test (SEM) conducted with the use of optical microscope Reichert and scanning microscope Hitachi S-4200. There occurred solution's dendrites α(Al), eutectic silicon crystal (β) and two types of eutectic solution: double eutectic α(Al)+β(Si) and multi-component eutectic α+AlSiCuNiMg+β.
The paper presents the influence of modification with phosphorus (CuP10) on the tribological properties of the alloy AlSi17Cu5Mg coupled abrasively with cast-iron EN GJL-350. Tests of coefficient of friction and wear of mass were conducted on tribological tester T-01. An important aspect in the assessment of the tribological properties is the analysis of initial material microstructure in reference to silumin which underwent modification with phosphorus. It was found that the difference in structure of tested materials, mainly sizes of primary silicon crystals significantly influences the tribological properties whereas the speed change of the friction knot does not have such big influence.
The paper presents an analysis of the effect of shape of primary silicon crystals on the sizes of stresses and deformations in a surface layer of A390.0 alloy by Finite Elements Method (FEM). Analysis of stereological characteristics of the studied alloy, performed based on a quantitative metallographic analysis in combination with a statistical analysis, was used for this purpose. The presented simulation tests showed not only the deposition depth of maximum stresses and strains, but also allowed for determining the aforementioned values depending on the shape of the silicon crystals. The studied material is intended for pistons of internal combustion engines, therefore the analysis of the surface layer corresponded to conditions during friction in a piston-cylinder system of an internal combustion engine having power of up to 100 kW. The obtained results showed important differences in the values of stresses and strains up to 15% between various shape of the silicon crystals. Crystals with sharp edges caused higher stresses and deformation locally than those with rounded shapes.
This paper presents the results of hypoeutectic 226 grade alloy as well as prepared on its basis Al-Si alloy containing Cr, V and Mo. The additives tested were added as AlCr15, AlV10 and AlMo8 master alloys. Alloys tested were poured into DTA sampler as well as using pressure die casting. An amount of Cr, V and Mo additives in alloy poured into DTA sampler comprised within the range approximately 0.05-0.35%. Alloys to pressure die casting contained 0.05-0.20% Cr, V and Mo. The crystallization process was examined using the derivative thermal analysis (DTA). The microstructure of castings made in the DTA sampler as well as castings made with use of pressure die casting were examined. The basic mechanical properties of castings made using pressure die casting were defined too. It has been shown in the DTA curves of Al-Si alloy containing approximately 0.30 and 0.35% Cr, Mo, and V there is an additional thermal effect probably caused by a peritectic crystallization of intermetallic phases containing the aforementioned additives. These phases have a morphology similar to the walled and a relatively large size. The analogous phases also occur in pressure die casting alloys containing 0.10% or more additions of Cr, V and Mo. The appearance of these phases in pressure die casting Al-Si alloys coincides with a decrease in the value of the tensile strength Rm and the elongation A. It has been shown die castings made of Al-Si alloys containing the aforementioned additives have a higher Rm and A than 226 alloy.