Effects of Heat Treatment on the Microstructure and Hardness of A356 (AlSi7Mg0.3) Manufactured by Vertical Centrifugal Casting

The A356 alloy has been widely used in automotive components, such as wheels and brake disks, because it is an excellent lightweight material with high corrosion resistance and good mechanical properties. Recently, to reduce the weight of brake disks, the Fe-A356 hybrid brake disk has been suggested. Because brake disk quality is directly related to driving safety, the T4/T6 heat treatment of centrifugally cast A356 alloys were performed to enhance the mechanical properties and reduce micro-segregation. The solid-solution heat treatment followed by annealing caused the formation of Mg-rich intermetallic compounds on the grain boundaries of the Al matrix, decreasing the average hardness of the alloys by 13 HV. In contrast, the solid solution followed by water quenching (T4) reduced the area fractions of the intermetallic compounds and increased the average hardness by 11 HV. The T6 heat-treated A356 alloys, which were influenced by the formation of the Guinier–Preston zone exhibited a relatively higher average hardness, by 18 HV, compared to T4 heat-treated A356 alloys.

Influence of stress state of brake disk on parameters of microgeometry of its surface that is out of contact area

The paper shows results of the study dedicated to influence of contact area stress state on a trend of changes for roughness and waviness parameters of brake disc surface located on the periphery of contact with a brake pad in the coverage area of preferred compression and tensile stresses. It also displays that the main trend of surface deformation under the influence of growing mechanical compression stresses consists in increase of altitude and decrease of step parameters of roughness and waviness. The authors have established that in the coverage area of tensile stresses the roughness and the waviness of the brake disk surface returns to initial values determined in condition of absence of external power influence. On the basis of the results, the authors have explained the process of waviness appearance on the brake disc surface. Results of the study are recommended for the application at solving tasks on friction and wear.

Local Heat Transfer Distributions Within a Rotating Pin-Finned Brake Disk

This study presents local temperature and heat transfer coefficient distributions obtained experimentally on the internal surfaces of a rotating pin-finned brake rotor at realistic rotation speeds for braking (i.e., N = 100–300 rpm). To this end, the thermochromic liquid crystal technique in a rotating reference frame was employed. The results demonstrate that the bulk airflow within the ventilated channel of a rotating disk follows a predominantly backward sweeping inline-like path between the pin fins. Internal local heat transfer is distributed nonuniformly on both inboard and outboard surfaces, with twice higher average cooling from the outboard surface than the inboard surface: this possibly exacerbates the thermal stresses, which leads to thermal distortion of the rotor (i.e., coning).

Three-dimensional coupled thermo-mechanical analysis for fatigue failure of a heavy vehicle brake disk: Simulation of braking and cooling phases

In this paper, transient coupled thermo-mechanical finite element analysis of a three-dimensional model of braking pairs (brake disk and brake pads) is accomplished in order to estimate temperatures and stresses in brake disk during a braking cycle, including braking and cooling phases, and calculate fatigue life. A nonuniform distribution of temperatures is revealed on the surface of the brake disk, gradually generating surface hot spots and hot bands with temperatures up to 800 °C that lead to an uneven distribution of thermal stresses on the frictional surfaces. According to the simulations, variations in the circumferential stress, which is mainly responsible for the cracking of the brake disk, can reach up to 400 MPa in the hot spot areas, depending on the braking configurations. The numerical results are also used to estimate the fatigue life of brake disk using the Smith–Watson–Topper model. The numerical model demonstrates a high accuracy of fatigue life estimation when evaluated by prior experimental studies, signifying the effects of hot spots in reducing the service life of brake disk. Results of the fatigue life estimation show superiority to the analytical method both in the accuracy of calculation and detection of the failure location.