Effect of Growth Velocity and Zn Content on Microhardness in Directionally Solidified Al-Zn Alloys

In this study, Al-xZn (x=1, 3, 5, 7, 10 and 20 wt. %) alloys were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified upward with a constant temperature gradient, G (10.3 K/mm) and different growth velocities (V) between 8.25 and 165 µm/s in the directional solidification apparatus. The experimental results have revealed that with the increase of the growth velocity of the melts from 8.25 µm/s to 165 µm/s, the microstructures undergo a transition from cellular/cellular dendritic morphology to coarse dendritic form for each composition (Zn content, Co). The measurements of microhardness (HV) of the specimens were performed by using a microhardness test device. The dependence of HV on V and Co was analyzed, and it has been found that with increasing the V and Co the HV increases. Relationships between HV-V and HV-Co were obtained by linear regression analysis, and the experimental results were compared with the results of previous similar works.