Feng Xia

Effect of Tin on Microstructure and Electrochemistrical Properties of Mg-Al-Sn-Zn Magnesium Alloys Anodic Materials

Morphologies, microstructure and composition distribution of the magnesium anodic materials were studied by metallographic microscopy, x-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The corrosion behavior and electrochemical properties of Mg alloy were also investigated by constant current method, potential polarization, collecting gas through drainage. The results show that tin restrained β-Mg17Al12 phase precipitation along the grain boundary. With the content of tin increasing, granular Mg2Sn phase was improved. After uniform heat treatment, most of β-Mg17Al12 phase was dissolved, but most of Mg2Sn was not dissolved. Tin could improve self-corrosion potential and release hydrogen rate. Magnesium alloy anode with 1% tin content had high discharge potential and current efficiency. With the current density increasing, the release hydrogen rate augmented. The current efficiency reached 82 % at 20mA/cm2. The main composition of the corrosion products were MgO and Al2O3 which were easily peeled off. As a result, more negative and stable work potential was produced and the reaction was accelerated continuously.

Microstructure Evolution and Mechanical Properties of an Al-Si-Cu-Mg-Ni Aluminium Alloy after Thermal Exposure

The microstructures and mechanical properties of an Al-Si-Cu-Mg-Ni aluminium alloy have been investigated after thermal exposure at 350 °C for time intervals up to 1000 h. Experimental results showed that, with increasing the thermal exposure time, room temperature ultimate tensile strength, elevated temperature ultimate tensile strength, and Brinell hardness firstly decreased remarkably (up to 100 h) and then decreased slightly to a certain constant value (100-1000 h). Before thermal exposure, room temperature ultimate tensile strength, elevated temperature ultimate tensile strength, elevated temperature elongation percentage, and Brinell hardness of the alloys are 203.5 MPa, 48.7 MPa, 9.2%, and 82.3, respectively. With increasing the thermal exposure time, eutectic silicon grows up steadily, and the amount of Q phase with a flower shape increases. Transmission electron microscopy analysis showed that the formation of stable θ precipitates was found in the microstructure.

Effects of Solidification Cooling Rate on the Microstructure and Mechanical Properties of a Cast Al-Si-Cu-Mg-Ni Piston Alloy

The effects of cooling rate 0.15, 1.5, 15, 150, and 1.5 × 105 °C/s on the microstructures and mechanical properties of Al-13Si-4Cu-1Mg-2Ni cast piston alloy were investigated. The results show that with an increase of solidification cooling rate, the secondary dendrite arm spacing (SDAS) of this model alloy can be calculated using the formula D = 47.126v − 1/3. The phases formed during the solidification with lower cooling rates primarily consist of eutectic silicon, M-Mg2Si phase, γ-Al7Cu4Ni phase, δ-Al3CuNi phase, ε-Al3Ni phase, and Q-Al5Cu2Mg8Si6 phase. With the increase in the solidification cooling rate from 0.15 to 15 °C/s, the hardness increased from 80.9 to 125.7 HB, the room temperature tensile strength enhanced from 189.3 to 282.5 MPa, and the elongation at break increased from 1.6% to 2.8%. The ε -Al3Ni phase disappears in the alloy and the Q phase emerges. The δ phase and the γ phase change from large-sized meshes and clusters to smaller meshes and Chinese script patterns. Further increase in the cooling rate leads to the micro hardness increasing gradually from 131.2 to 195.6 HV and the alloy solidifying into a uniform structure and forming nanocrystals.

Nanophase formation during the heat treatment of Al-13Si-5Cu-2Ni-1Mg alloy and the abnormal enhancement of its tensile properties

Abstract Two T6 (500°C × 3 h, water quenching and 210°C × 6 h, air cooling) samples of Al-13Si-5Cu-2Ni-1Mg alloy were furture heated to 350°C and 420°C, respectively for various times. The tensile strength of the alloy, measured at both room temperature and 350°C is observed to abnormally increase, especially for the samples that were heated to 420°C. Al11Cu5Mn3 nanoparticles that form stably during these heating processes exhibit a higher volume fraction after the exposure to 420°C than that obtained by the exposure to 350°C. These nanoparticles were responsible for enhancing the alloys tensile properties because of the precipitation strengthening effect of the second nano-phase.