Penghuai Fu

Solidification Microstructure and Mechanical Properties of Cast Magnesium-Aluminum-Tin Alloys

The solidification microstructure and mechanical properties of as-cast Mg-Al-Sn alloys have been investigated using computational thermodynamics and experiments. The as-cast microstructure of Mg-Al-Sn alloys consists of α-Mg, Mg17Al12, and Mg2Sn phases. The amount of Mg17Al12 and Mg2Sn phases formed increases with increasing Al and Sn content and shows good agreement between the experimental results and the Scheil solidification calculations. Generally, the yield strength of as-cast alloys increases with Al and Sn content, whereas the ductility decreases. This study has confirmed an early development of Mg-7Al-2Sn alloy for structural applications and has led to a promising new Mg-7Al-5Sn alloy with significantly improved strength and ductility comparable with commercial AZ91 alloy.

Zr-Containing Precipitates in Mg-3wt%Nd-0.2wt%Zn-0.4wt%Zr Alloy during Solution Treatment at 540°C

The microstructure of Mg-3wt%Nd-0.2wt%Zn-0.4wt%Zr (NZ30K) alloy after solution treatment was investigated and several kinds of interesting phases containing zirconium were found in this study. NZ30K was gravity cast using permanent die casting. After high tempering solution treatment at 540°C, cluster particles were observed inside the grains under optical microscopy. The detailed investigations were carried out on transmission electron microscopy (TEM). Four kinds of precipitates were visible inside grains with different shapes: block-like, globular, short rod-like, long rod-like. The block-like particle was identified as ZrH2 phase and the globular one was Zn2Zr3 phase. The other two were still Zr-containing phases, which could not be identified to any of existed compounds containing Zr. The formation of Zn-Zr compounds would probably be due to relative high ratio of Zr to Zn in the center of grains. ZrH2 would be the results of reaction of zirconium with H element during solution treatment, which probably came into the alloy during melting.

Study on microstructure of squeeze casting AZ91D alloy

Abstract The present paper reports the investigation of the microstructure distribution of squeeze cast AZ91D alloy. The microstructure of squeeze cast AZ91D alloy is not uniform and is composed of four zones, which are chilled layer, segregation zone, pressured crystallisation area and hot spot area respectively. Moreover, in the pressured crystallisation area, the microstructure sequence in the transverse section from the outside to the inside could be divided into four sublayers, such as fine equiaxial dendrite area, dendrite area with a high directivity, confusion dendrite area and disorder dendrite area. The volume fraction of the intermetallic compound Mg17Al12 also varied with the location. The volume fraction of Mg17Al12 in the pressured crystallisation area is the largest except in the segregated zone.

Ductility Improvement of Mg-Nd-Zr Cast Alloy by Trace Addition of Zn

This paper reports a significant increase in tensile ductility in solution-treated Mg-Nd-Zr cast alloy by trace addition of 0.2wt.% Zn. The improvement is accompanied by the occurrence of wavy slip lines on the surface of fractured tensile specimens, which are caused by the activation of non-basal slips including and or non-basal dislocations, while these non-basal slips are hardly observed in Mg-Nd-Zr alloy without Zn addition.

Effect of process parameters on structure and macrosegregation upon direct chill casting of Mg–Nd–Zn–Zr alloy

Abstract Direct chill (DC) semicontinuous casting process has been successfully used to produce sound Mg–3·0Nd–0·4Zn–0·4Zr (NZ30K) billets. The influence of process parameters such as casting speed, casting temperature on the microstructure and macrosegregation was studied. The results show that the casting speed affects the macrosegregation greatly while it has a slight influence on the grain size of the billet; the casting temperature has a slight influence on macrosegregation of the billet while the grain size of the billet increases as the casting temperature increases. The optimal process parameters have been experimentally determined as follows: casting temperature 700°C and casting speed 90 mm min−1. The ultimate tensile strength, yield strength and elongation of billets cast at the optimal casting parameters are 196 MPa, 125 MPa and 16·5% respectively.

Study on the Microstructure and Mechanical Property of High Strength Mg-Nd-Zn-Zr Alloy

The microstructure and mechanical properties of Mg-3wt％Nd-0.2wt％Zn-0.4wt％Zr alloy in as-cast, solution-treated and solution-treated + peak-aged were investigated. The alloy had a cast structure with large intergranular Mg12Nd phase between the α-Mg matrix. After solution-treated, the intergranular Mg12Nd phase disappeared and lots of small Zr-containing particles distributed inside the grains. Small plate-like phases precipitated inside the grains strengthened the alloy to a high level after peak-aged at 200°C for 16 hours: the ultimate strength of the alloy up to 305 MPa, with considerable elongation rate 11%, and yield strength 140 MPa. The peak-aged samples also had good creep resistance, with strain rate less than 0.2% after 120 hours creep test under the condition of 110 MPa at 200°C. The minimum creep rate was about 4.64×10-9. The alloy had different fracture pattern in different states: as-cast state, intergranular fracture was the key pattern to failure; after solution-treated, the fracture pattern turned to cleavage transgranular fracture; after peak-aged, the alloy had a mixed fracture pattern of transgranular and intergranular, in which transgranular was the main style.

Microstructure and Mechanical Properties of Low Pressure Die Cast AM50 Magnesium Alloy

Compact AM50 alloy components were cast by Low Pressure Die Casting (LPDC) process. The microstructure and mechanical properties of cast components were investigated under as-cast and heat treated states. It was found that the microstructure of LPDC AM50 is composed of α-Mg and second phases - Mg17Al12 and Al8Mn5. Compared with Gravity die casting, LPDC AM50 alloy had much coarser grains and higher density, with smaller sizes and less content of second phases. The density of AM50 alloy by LPDC process was ρ=1.7836g/cm3, with increase of 0.45% based on Gravity die casting and much more increase compared with high pressure die casting. The as-cast mechanical properties by LPDC process were: σ0.2=57.8Mpa, σb=192.3Mpa, δ=8.7%. These of Gravity die casting were: σ0.2=53Mpa, σb=173.4Mpa, δ=8.1%. UTS in LPDC increased about 20MPa, with better YTS and Elongation. Compared with that of high pressure die cast AM50, the YTS of LPDC was much lower, with comparable UTS and Elongation. The mechanical properties of the heat treated AM50 alloy were still in the same level of as-cast state. AM50 alloy by LPDC process is not necessary subjected to tempering treatment.

Optimization of Magnesium‐Aluminum‐Tin Alloys for As‐Cast Microstructure And Mechanical Properties

The microstructure and mechanical properties of as-cast Mg-Al-Sn alloys have been investigated using computational alloy design and experimental approaches. The as-cast microstructure of Mg-Al-Sn alloys consists of α-Mg, Mg17Al12 and Mg2Sn phases. The volume fractions of Mg17Al12 and Mg2Sn phases increase with increasing Al/Sn contents, and show good agreement between computational thermodynamics modeling and the experimental results. Generally, the yield strength of as-cast alloys increases with Al/Sn alloying contents, while the ductility decreases. This study has confirmed an earlier development of Mg-7Al-2Sn alloy and led to a promising new Mg-7Al-5Sn alloy with significantly improved strength and ductility compared to commercial alloy AZ91 (Mg-9Al-1Zn).

Application of Electrochemical Techniques to Characterization of the Corrosion Behaviors of GW63 Alloys

The corrosion behavior of GW63 (Mg-6wt.%Gd-3wt.%Y-0.4wt.%Zr) alloys in 5% NaCl aqueous solution has been investigated by PARSTAT 2273 instrument. The Open Circuit Potential (ECORR) vs. time curve, cyclic polarization (Pitting Scans) curve and Electrochemical Impedance Spectroscopy (EIS) was measured for the GW63 alloys in as-cast and T6 heat treatment conditions. The EIS results indicated that the tendency of impedance variation for as-cast condition was monotonic decreasing, however, the tendency of variation for T6 condition was not completely monotonic but the total tendency was decreasing. The values of impedance of GW63 alloy at 0.1 Hz are about 103 ohm-cm2 for as-cast and T6 condition.