Effect of Modifier Form on Mechanical Properties of Hypoeutectic Silumin

Abstract

Aluminum–silicon alloys require modification due to their coarse-grained microstructures and resulting low strength properties. So far, research into the modification process has focused on the use of various chemical components and technological processes, the tasks of which are to refine the microstructure and, thus, increase the mechanical properties of the alloy. In this paper, the answer to the question of whether the form of the modifier influences the modification effect of the hypoeutectic silumin will be found. The tests were carried out using the popular silumin AlSi7Mg. To answer our research question, the alloy was modified under comparable conditions using the following elements: Ti, B, and master alloys AlTi1.5 and AlB1.5. Modifiers in the form of Sr and master alloy AlSr1.5 were also used. All mentioned modifiers were produced and introduced into the liquid alloy in the form of a powder and a rod. Master alloys AlSr1.5 were also produced via cooling from the liquid state through cooling in air and the second variant at a speed of 200 °C/s (in the form of powder and a thin strip). The microstructure and mechanical properties were analyzed based on the following measures: tensile strength, elongation, and hardness of silumin. Based on the conducted research, it was found that the form of the modifier also affects the modification effect visible in the form of changes in the microstructure and mechanical properties. For the powder-modified alloy, greater fineness in the eutectic phase (α and B phases) and an increase in all analyzed mechanical properties were obtained.