Research On The Structure And Properties Of Rheological Squeeze Casting Of High-Strength Al-11zn-1.84mg-0.92cu-0.15zr-0.15sc Alloy

As the manufacturing of structural parts in the fields of aerospace, rail transit, automobiles, and national defense and military industries develops in the direction of integration and large-scale development, the demand for large-scale lightweight structural parts is increasing day by day, and there is a trend of using high-performance aluminum alloys to replace steel materials. . Al-Zn-Mg-Cu alloy has the characteristics of high strength and high toughness, and is one of the preferred materials for lightweighting. However, this type of highly alloyed aluminum alloy is usually a deformed aluminum alloy with poor casting performance, large solidification temperature range, and shrinkage. Due to serious problems such as segregation and hot cracking, it cannot be directly cast and formed. The performance must be improved through multiple processes such as casting, plastic deformation, and machining before it can be used. The processing cost is high, which greatly limits the wide application of the alloy.

Semi-solid rheological casting technology combines the semi-solid slurry process with the traditional casting process and has many technical advantages, such as improved filling capacity of the semi-solid slurry, fine and uniform structure of the cast after forming, significant improvement in segregation, and solidification of the casting. The degree of shrinkage is small, the tendency of thermal cracking is small, and the mechanical properties are significantly improved. However, the Al-Zn-Mg-Cu alloy currently studied on rheological forming is a 7xxx series deformed aluminum alloy. Although the semi-solid rheological casting process can improve the thermal cracking resistance of the alloy to a certain extent, it is difficult to meet the requirements for large-scale Forming requirements for complex castings.

On the basis of previous research, the research team of Youyan Composites Senior Engineer Zhang Zhifeng selected Al-11Zn-1.84Mg-0.92Cu-0.15Zr-0.15Sc alloy as the research object and used rheological extrusion casting to study the hot cracking of the alloy. Sensitive properties and the structure and mechanical properties of rheological squeeze castings are used to prepare high-performance orbital castings with mechanical properties close to or exceeding the requirements of similar deformation alloys, in order to provide technology for the engineering application of ultra-high-strength aluminum alloy rheological squeeze castings. refer to.

Zhang Zhifeng is a senior engineer and doctoral supervisor at Beijing Nonferrous Metals Research Institute. He received his doctorate in materials processing from Dalian University of Technology in 2001. He has long been committed to the research of advanced controlled solidification and semi-solid precision forming technology of aluminum alloys and their composite materials for more than 20 years. He has formed distinctive research characteristics in electromagnetic control of solidification structure refinement and uniformity. He has published more than 200 academic papers and has been authorized by the state. It has more than 50 patents and 5 provincial and ministerial level science and technology awards. He also serves as a member of the editorial board of Special Casting and Nonferrous Alloys Magazine.

[Image and text content]

Using self-configured aluminum alloy, the raw materials are high-purity aluminum ingots (99.99%, mass fraction, the same below), high-purity magnesium ingots (99.95%), high-purity zinc ingots (99.92%), Al-50Cu, Al-10Zr and Al-2Sc The composition of the master alloy ingot was detected using the FOUNDRY-MASTER Pro electric spark direct reading spectrometer, and the Sc content in the alloy was measured through the chemical composition analysis method of deformed aluminum and aluminum alloys in GB/T17432-1998. The actual chemical composition of the alloy is shown in the table 1. The alloy is smelted using a resistance heating furnace. The melting crucible is made of high-purity graphite. The melting temperature is controlled at 760°C. The alloy melt is degassed and slag-removed by rotating argon gas. The melt temperature is controlled at about 720°C and left to stand. .

Table 1 Actual chemical composition of test alloy (%)

Figure 1 Actual picture of the rheological squeeze casting device and track parts

1. Temperature collector 2.K type thermocouple 3. Melt 4. Crucible 5. Stirring coil

Figure 2 Sampling location diagram for track component structure observation and mechanical property testing

Figure 3 The actual hot cracking test rods of the test alloy and 7075 alloy and the corresponding calculation results of the hot cracking sensitivity index

No obvious hot cracks were observed in the two shorter hot-cracked rods of the test alloy. Cracking only occurred near the sprue openings and restraining balls of the two longer hot-cracked rods. Most of the cracks were slight cracks, and no complete fracture was found. . In Figure 3b, serious cracks appeared at the sprue opening of the longest hot cracking rod of the 7075 alloy sample, and slight cracks appeared at the sprue opening and restraining ball of the second-longest hot cracking rod. Therefore, the thermal cracking resistance of the test alloy Sensitivity better than 7075 alloy

Figure 4 OM structure of samples at different positions of extrusion cast track parts before and after electromagnetic stirring

Figure 5 Grain size of extrusion cast track parts before and after electromagnetic stirring treatment

Figure 6 SEM images of the structure of extrusion cast track parts at different positions before and after electromagnetic stirring treatment

Figure 7 EDS analysis of the unresolved phase of alloy T6 after heat treatment in Figure 6a

Figure 8 Mechanical properties of extrusion cast track parts before and after electromagnetic stirring treatment

【Analysis conclusion】

(1) Al-11Zn-1.84Mg-0.92Cu-0.15Zr-0.15Sc alloy has good resistance to thermal cracking sensitivity. After electromagnetic stirring melt treatment, the grains of extrusion cast rail parts are fine and uniform, and the grain boundaries are The number of coarse primary Al3 (Sc, Zr) phase and low melting point eutectic phase decreases, and the size decreases significantly.

(2) After T6 heat treatment, the low melting point eutectic phase is almost completely dissolved back into the matrix, and the mechanical properties of the casting are significantly improved. The average tensile strength reaches 565 MPa, the elongation is 7.5%, and the mechanical properties are consistent and stable. Sexuality is significantly improved.

[Literature citation]

Xu Yongtao, Zhao Purui, Bai Yuelong, et al. Research on the rheological squeeze casting structure and properties of high-strength Al-11Zn-1.84Mg-0.92Cu-0.15Zr-0.15Sc alloy [J]. Special Casting and Nonferrous Alloys, 2023, 43(6) :763-767.

XU Y T,ZHAO P R,BAI Y L,et al.Microstructure and mechanical properties of rheo-squeeze casting of high strength Al-11Zn-1.84Mg-0.92Cu-0.15Zr-0.15Sc Alloy[J].Special Casting & Nonferrous Alloys, 2023,43(6):763-767.