Effect of Heat Treatment on Microstructure and Mechanical Properties of Si Cp/2024 Aluminum Matrix Composite

SiCp/2024 aluminum alloy matrix composite was prepared by powder metallurgy method. Effects of heat treatment on the microstructure and mechanical properties of composite were investigated by SEM, EDS, XRD, HREM, tensile and hardness tests. The experimental results showed that SiC particles distributed uniformly in the matrix and were in good combination with matrix. The tensile strength and hardness were improved significantly after heat treatment. With the increase of solid solution temperature, the alloy phases dissolved in the matrix gradually. When the solid solution temperature arrived at 505 ℃, the alloy phases dissolved thoroughly, and the composite exhibited the highest tensile strength and hardness（σb=360 MPa, HBS=104）. The main strengthening phase was Al2Cu, which was granular and distributed dispersively in the matrix. Effect of T6 was better than that of T4 at the same solid solution temperature.

Effect of Post-weld Heat Treatment on Mechanical Characteristics of AZ31 Magnesium Alloy Welded Joints

Tungsten inert gas（TIG） welding was performed on 2.7 mm thick commercial extruded AZ31 B magnesium alloy plates. We investigated the effect of post-weld heat treatment（PWHT） on the microstructure, mechanical properties and precipitated phase of the weld joints. The results showed that during the annealing treatment（200 ℃-1 h, 250 ℃-1 h, 300 ℃-1 h, 350 ℃-1 h, 400 ℃-1 h, and 450 ℃-1 h）, the average grain size in the weld seam was the minimum after annealing at 400 ℃ for 1 hour, and then abnormally grew up after annealing at 450 ℃ for 1 hour. The mechanical properties enhanced when the joints were processed from 200 ℃-1 h to 400 ℃-1 h but sharply decreased with increasing annealing temperature. In contrast to the annealing treatment, solution treatment（250 ℃-10 h, 300 ℃-10 h, 350 ℃-10 h, 400 ℃-10 h, and 450 ℃-10 h） exhibited a better ductility but a slight deterioration in tensile strength. Especially speaking, no eutectic compounds（such as Mg17 Al12） were observed in the weld seam. The supersaturated Al atoms were precipitated in a coarse spherical shape dispersed in the weld seam. The precipitated Al atoms dissolved in the matrix substances at the condition（400 ℃-1 h） or（250 ℃-10 h）. The solution treatment caused grain coarsening and precipitated Al atoms dissolved in the weld seam substantially, which resulted in a drop in micro-hardness at the weld seam compared to the area of the annealed joints.

Synergistic effects of composition and heat treatment on microstructure and properties of vacuum die cast Al-Si-Mg-Mn alloys

The purpose of this study was to prepare high-quality Al-Si-Mg-Mn alloy with a good combination of strength and ductility employing the vacuum-assisted high-pressure die cast process. An orthogonal study of heat treatments was conducted to design an optimized T6 heat treatment process for both Al-10%Si-0.3%Mg-Mn and Al-11%Si-0.6%Mg-Mn alloys. The results demonstrate that no obvious blisters and warpage were observed in these two alloys with solid solution treatment. After the optimal T6 heat treatment of 530°C×3 h + 165°C×6 h, Al-11%Si-0.6%Mg-Mn alloy has better mechanical properties, of which tensile strength, yield strength and elongation reached 377.3 MPa, 307.8 MPa and 9%, respectively. The improvement of mechanical properties can be attributed to the high density of needle-like β″(Mg_5Si_6) precipitation after aging treatment and the fine and spherical eutectic Si particles uniformly distributed in the α-Al matrix.

Microstructure and stress-rupture property of an experimental single crystal Ni-base superalloy with different heat treatments

The influence of heat treatment on the microstructure and stress-rupture property at 1,100 °C/140 MPa was investigated in a 5.0 wt% Re containing experimental single crystal Ni-base superalloy. The results indicate that the γmorphology is nearly cuboidal in the dendrite core after conventional heat treatment. The lattice misfit of alloy becomes more negative after modified heat treatment and results in more cuboidal γ precipitates than that after conventional heat treatment. The increased stress-rupture life after modified heat treatment is attributed to higher γ volume fraction, more negative lattice misfit, well-rafted structure, and narrower c channel width.

Effect of friction stir processed microstructure on tensile properties of an Al-Zn-Mg-Sc alloy upon subsequent aging heat treatment

An as-cast Al-Zn-Mg-Sc alloy was friction stir processed varying tool related parameters, yielding microstructures with different grain sizes （0.68, 1.8 and 5.5 μm）. Significant increases in room temperature ductility were obtained in these materials with reasonable enhancement in strength. It is demonstrated that the type of microstructure produced by friction stir processing （FSP） has a significant influence on the choice of post-FSP heat treatment design for achieving improved tensile properties. It is also found that the ultrafine grained FSP material could not achieve the desired high strength during the post-FSP heat treatment without grain coarsening, whereas the micro-grained FSP materials could reach such strength levels （〉560 MPa） under conventional age hardening heat treatment conditions.

Effects of Heat Treatment on Surface Recrystallization and Stress Rupture Properties of a Fourth-Generation Single-Crystal Superalloy after Grit Blasting

The specimens of a fourth-generation single-crystal superalloy were grit-blasted and heat-treated in vacuum at 1100, 1150, 1200, 1250 and 1300 °C for 4 h, respectively. Then, the microstructure and the stress rupture properties of the recrystallized alloy were investigated at 1150 °C/120 MPa. The results showed that a cellular recrystallization occurred in the surface layer after heating at 1100, 1150 and 1200 °C for 4 h. An equiaxed recrystallization formed as the specimen was heat-treated at 1300 °C for 4 h, while a mixed recrystallization occurred in the specimen heat-treated at 1250 °C for 4 h. The recrystallized depth clearly increased with a rise of the heat treatment temperature. The stress rupture life continuously decreased with a rise of the heat treatment temperature up to 1250 °C. Although the overall stress rupture life reduced to different degrees, the stress rupture life of specimen after heat treatment at 1300 °C was relatively high and intermediate between those of specimens treated at 1150 and 1200 °C. The fact that the stress rupture life reduced to different degrees after heat treatment can be attributed to the recrystallization of the surface layer and to the microstructure evolution of the interior of the specimen. The small γ’ phase precipitated again after heat treatment at 1300 °C for 4 h. So,the stress rupture life was relatively longer than that after heat treatment at 1200 or 1250 °C although the equiaxed recrystallization formed in the surface layer.

A study of microstructure and properties of cast Fe-10Cr-1.5B alloy

In the present study, the microstructure and mechanical properties of cast Fe-10Cr-1.5B（FCB） alloy after different heat treatments were studied. The results showed that the as-cast microstructure of FCB alloy consists of α-Fe, M（M=Cr, Fe, Mn）2（B, C） and M（M=Cr, Fe, Mn）7（C, B）3 type borocarbides, and small amounts of pearlite and austenite. After oil quenching treatment, metal matrix transformed into the martensite from the mixture of martensite, pearlite and austenite. There are many M（M=Cr,Fe,Mn）23（C,B）6 type borocarbide precipitates in the metal matrix, and eutectic borocarbide appears with an apparent disconnection and isolated phenomenon. When the quenching temperature reaches 1,050℃, the hardness of FCB alloy is the highest, but the change of quenching temperature has no obvious effect on impact toughness of FCB alloy. After tempering, the eutectic microstructure of FCB alloy appears with a ＂two links＂ trend. With the increase of tempering temperature, the hardness of FCB alloy decreases gradually and impact toughness increases gradually. Cast FCB alloy oil-quenched from 1,050℃ and tempered from 200℃ has excellent combined properties; its hardness and impact toughness are 61.5 HRC and 8.8 J·cm^-2 respectively.

Effects of Cr Content on the Microstructure and Properties of 26Cr–3.5Mo–2Ni and 29Cr–3.5Mo–2Ni Super Ferritic Stainless Steels

By using scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, strength and hardness measurements, the microstructure, precipitation, mechanical properties, and corrosion resis- tance have been investigated for two super ferritic stainless steels, 26Cr-3.SMo-2Ni and 29Cr-3.5Mo- 2Ni, with the aim to consider the effect of Cr content. The results showed that with the addition of Cr content, the recrystallization temperature was increased; the precipitation of Laves and Sigma （o） phases was promoted and the mechanical properties of super ferritic stainless steel were modified. Further- more, the pitting corrosion resistance and corrosion resistance to H2SO4 of the two super ferritic stainless steels were improved. In addition, suitable annealing processing is a key factor to maintain integrated performance by optimizing microstructure and removing detrimental precipitation phases.

Effects of substitution of Nd in a sand-cast Mg-2.5Nd-0.6Zn-0.5Zr alloy with x wt.% Sm(x=2.5, 4, and 6)

The microstructures and mechanical properties of a series of sand-cast Mg-Sm-Zn-Zr alloys under ascast, solution-treated and peak-aged states were thoroughly investigated. The OM, XRD, SEM and HRTEM were employed to characterize the microstructural evolution. The results indicate that substitution Nd in the conventional Mg-2.5 Nd-0.6 Zn-0.5 Zr alloy with different contents of Sm has comparative grain refinement effect and will fully change the dominant intermetallic phase. In addition, the substituted alloys perform clearly higher strength with comparative ductility at both as-cast and peakaged conditions and much greater aging hardening response than the referential alloy. It is obvious that the strength increments of this alloy are attributed to the changes of the eutectic intermetallic particles on grain boundaries.