Hengcheng Liao

Correlation between mechanical properties and amount of dendritic α-Al phase in as-cast near-eutectic Al–11.6% Si alloys modified with strontium

Abstract The amount of dendritic α-Al phase with varying Sr content in near-eutectic Al–11.6% Si alloy was measured by quantitative metallography analysis software and the correlation of mechanical properties of fully modified alloy with the amount of dendritic α-Al is discussed. Addition of Sr in Al–Si alloys results in a considerable increase of the amount of α-Al. Mechanical properties of the fully modified alloy are linearly related to the volume fraction of dendritic α-Al, which plays a key role in improving the mechanical properties of near-eutectic Al–Si alloys.

Laser bending of friction stir processed and cement-coated sheets

ABSTRACT In this work, laser bending of friction stir processed and cement-coated sheets of aluminum alloy and mild steel was carried out using CO2 laser. For comparison, the laser bending of uncoated raw sheets was also carried out. It was noted that friction stir processing roughened the surface and helped in getting larger bend angle due to increased absorptivity in laser bending. However, the cement-coated sheets provided much larger bend angles. The micro-hardness of friction stir processed sheets was larger compared with unprocessed sheets and it further increased after laser bending. After laser bending, the micro-hardness increased from bottom surface to irradiated top surface. It was always more than the micro-hardness of the raw sheet. A study of microstructures revealed that the grain size reduced after laser bending and increased from top irradiated surface to bottom surface.

Effect of Quenching Wait Time on Microstructure and Mechanical Properties of As-Extruded AA6063 Alloy

Effect of quenching wait time after hot extrusion on microstructure and mechanical properties of AA6063 alloy was investigated by optical microscopy observation, tensile and Brinell hardness tests. Results show that the quenching wait time has an important influence on the microstructure and mechanical properties of AA6063 alloy. During hot extrusion, dynamic recrystallization occurs only in local areas suffered much larger strains, however, only within 10s’ wait time after extrusion, the static recrystallized grains have maturely developed. After subsequent T6 heat treatment, the recrystallized grains of the prompt-quenched sample are more uniform than that of the wait-quenched sample, and mechanical properties of the former are also better than that of the latter.

Effect of Ni Addition on the Solidification Process and Microstructure of Al-12%Si-4%Cu-1.2%Mn-x%Ni Heat-Resistant Alloys

By PandatTM phase diagram calculations based on Equilibrium and Scheil Models and microstructure observation by optical microscope, XRD and SEM-EDS, the effect of Ni addition in Al-12%Si-4%Cu-1.2%Mn-x%Ni heat-resistant alloys (in wt%; x = 0, 0.8, 2.0, 2.4, 3.4) on solidification process and microstructure is discussed in this study. Microstructure observation are in good consistence with the prediction from phase diagram calculation, except for the constituent of Ni-rich phase. Ni addition considerably changes the solidification process, not only enlarging the crystallization temperature range of primary Al15Mn3Si2 phase but also completely suppressing the two-phases eutectic reaction when Ni content is beyond 2 wt%. And it also results in an increase in the amount of primary Al15Mn3Si2 phase, and makes its morphology change from coarse dendrites to slender rods. In Ni1 (x = 0.8) and Ni2 (x = 2.0) alloys, fish-skeleton δ-Al3CuNi is found to be partially in coupled growth with blocky γ-Al7Cu4Ni phase, and in Ni3 (x = 2.4) and Ni4 (x = 3.4) alloy, new short-rod e-Al3Ni is formed.

Hardening Response to Rapid Aging Processes and Precipitation in Al-7%Si-0.3%Mg Alloy

An orthogonal test was designed to obtain a optimized rapid aging process in order to shorten aging time. Hardness and tensile tests and TEM observation were used to evaluate the hardening response to the rapid aging process. An optimized rapid aging process, 160°C2h+200°C2h, is obtained. Under this process, the alloy has an approximately equal hardness and strength to the conventional single stage peak aging process, but the aging time of the rapid aging process is remarkably shortened, only 16.7% of the conventional process. Compared with the conventional aging process, the number density of β″ precipitates formed during the rapid aging course is reduced, however, the amount of β′ precipitates is remarkably increased. Though the contribution of the β″ precipitates to hardening is reduced, that of the high density of β′ rod precipitates is considerably increased, thus the rapid aging process produces an approximately equal hardening effect to the conventional peak aging process.