Casting structure of metals and alloys

，关于金属及合金的铸造组织。

Casting organization is one of the important basis to realize the casting quality. The purpose of studying the casting structure of metal and alloy is to further understand the performance, reliability, stability and other properties of metal and alloy. It is of great practical significance to realize the comprehensive use of metal and alloy.

The casting structure of metal and alloy is mainly determined by the cooling speed and cooling method. The rapid cooling or slow cooling of the molten metal will form different types of casting structures. The slower the cooling process, the more compact and uniform the casting structure will be; the faster the cooling process, the more coarse and uneven the casting structure will be. In addition, different cooling methods also lead to different casting structures, such as surface layer cooling, center layer cooling and whole body cooling.

When metal and alloy are cooled from solidified to room temperature, the actual cooling process involves the change from solidification structure to processing structure. The solidification structure is the structure of metal and alloy at the end of solidification, and the processing structure is the structure of metal and alloy after solidification. This process usually involves the change of macro-structure and micro-structure. Macrostructure refers to the visible structure under microscope, such as the three individual eutectic structures of hypereutectic aluminum-silicon alloy, and microstructure refers to the invisible structure of metal and alloy, such as the crystalline structure in hypereutectic aluminum-silicon alloy.

The casting structure of metal and alloy has some common features, such as fine and uniform grain size, concise and orderly arrangement, stable structure and uniform distribution. Depending on the type of metal and alloy, the casting structure can be divided into the following four categories: dendritic structure, ingot structure, eutectic structure and macrostructure.

Dendritic structure is a casting structure composed of metal and alloy grains with dendritic shape, which is the most common metal and alloy casting structure. The dendritic structure can be divided into two categories: incomplete dendritic structure and complete dendritic structure. The special shape of dendritic structure helps to improve the mechanical properties and thermal properties of metal and alloy.

The ingot structure is a casting structure with abundant metal and alloy grains and strong three-dimensional effect, which is characterized by loose arrangement and randomness. The ingot structure has a certain degree of creep resistance, which can effectively prevent metal and alloy from deformation under pressure.

The eutectic structure is a casting structure composed of two or more metal and alloy components. The characteristics of eutectic structure are fine and uniform grain size, concise and orderly arrangement, stable structure and uniform distribution. Such casting structure can improve the mechanical properties and thermal properties of metal and alloy.

The macrostructure is a casting structure with visible size, which can be divided into four categories: globular, dendritic, fibrous and intergranular. The macrostructure can effectively increase the plasticity and toughness of metal and alloy.

In conclusion, studying metal and alloy casting structure is of great significance to improve the performance and utilization of metal and alloy. Different types of casting structure have different effects on metal and alloy performance and utilization, therefore, it is necessary to study the casting structure of metal and alloy in depth.

Casting Organization of Metals and Alloys

Metals and alloys are materials that are difficult to process due to their relatively high elasticity and strength. They are used in many different applications, from manufacturing cars and aircraft to making medical implants and jewelry. Casting is a popular method for producing such products because it can produce intricate and complex shapes with excellent repeatability.

Casting is a manufacturing process in which a material is heated, poured into a mold, and allowed to cool to form a solid structure. The shape of the finished part depends on the size, shape, and geometry of the mold. Casting relies on a thermal gradient between the mold material and the molten metal to bring the latter into the desired shape. The organization of the metal in a casting depends on the rate of solidification, which is determined by the properties of the alloy and the heat transfer rate. The solidified particles within the casting form a solid structural skeleton or matrix that gives mechanical support to the surrounding material.

Casting organizations are classified according to the size and shape of the particles and the network of solid particles within the material. These are differentiated according to the shape of the particles and the orientation of the bonds between them. For example, primary dendrite structures involve the formation of elongated and branching particles which results in greater mechanical strength compared to other cast metals. Additionally, directional solidification may form columnar grains which align along the solidification direction for increased strength.

When casting metals, the cooling rate and solidification temperature should be carefully controlled to ensure that the desired microstructure and mechanical properties can be achieved. By tweaking the parameters of the process, engineers can create castings with superior mechanical properties and quality compared to other fabrication techniques.