Study On The Grain Refinement And Porosity Of Zn-22Al Alloy

ZnAl?Zn-22Al?eutectoid alloys have been widely used as engineering structural component to attenuate undesirable noise and mechanical vibration under dynamic working condition because of their high damping capacity.However,high damping performance is generally coupled with poor mechanical properties.In this dissertation,the microstructure of Zn-22Al alloys have been refined by Zr,Mn,La elements and a novel Al-5Ti-1B ribbon inoculant with the aim to enhance the mechanical properties while remaining its high damping capacity.An open-celled Zn-22Al foam with adjustable porosity and pore size has also been fabricated by air pressure infiltration method to further enhance its damping capacity.The experimental results indicated that a trace of Zr,Mn,La elements could refine the primary?-Al phase in Zn-22Al alloy effectively by forming an undercooled zone in front of the growing?-Al solid/liquid interface.Compared with commercial Al-5Ti-1B rod,the novel Al-5Ti-1B ribbon had better grain refining effect on Zn-22Al alloy due to its finer hexagonal TiB₂ and cubic L1₂-Al₃Ti particles.Combination addition of 0.3 wt.%Al-5Ti-1B ribbon and 0.1 wt.%Zr element could achieve the best grain refining effect.With decreasing the average grain size of?-Al phase,the mechanical properties including tensile strength,elongation and hardness increased gradually.While the damping capacity of refined Zn-22Al alloys showed different variation patterns within different temperature regions because of the synthetic effect of two opposite influencing factors.The increase in the number of phase interfaces and grain boundaries of?-Al owing to grain refinement could enhance the damping,while the decrease of mobility of various interfaces due to the compressive stress imposed by the neighboring lamellar and the pinning effects of second phase particles?La-rich compound,Mn-rich compound,TiB₂ and Al₃Ti?could decrease the damping.The open-celled porous Zn-22Al alloys fabricated by replication of NaCl space-holders exhibited three-dimensional interconnected network structure,and their pores distributed homogenously in the metal matrix.The compressive stress-strain curve of the porous Zn-22Al alloys could be distinctly divided into three stages including elasticity,plateau and densification.With the increase of porosity,the compressive strength gradually decreased of the porous Zn-22Al alloys.It was worth noting that by addting Zr,Mn and La elements or Al-5Ti-1B inoculant,the compressive strength of porous Zn-22Al alloys was remarkably enhanced,and the energy absorption ability and efficiency were also improved.Compared with unrefined porous Zn-22Al alloy,the damping of the refined ones showed lower values at relatively low temperatures,at relatively high temperatures,however,showed higher values.