For previous article, please refer to Die Casting Design Specifications—Basic Introduction.
This series mainly introduces specifications related to die-casting design, including an introduction to basic knowledge, material selection, structural design specifications, introduction to die-casting molds and materials, and how to self-check during structural design. Next, we will introduce them to you one by one. This article mainly introduces commonly used materials and selection of die castings. Details are as follows;
When mechanical engineers choose die-casting materials, they should reasonably select correct die-casting material based on various factors such as product performance, process performance, production conditions, economy, and characteristics of die-casting materials. Commonly used die-casting materials include aluminum alloys, zinc alloys and magnesium alloys.
Requirements for die-casting alloys are as follows:
1) Sufficient strength and plasticity at high temperatures, no thermal brittleness (or low thermal brittleness)
2) Keep linear shrinkage and crack tendency as small as possible to avoid cracks in die castings and ensure high dimensional accuracy of die castings.
3) Crystallization temperature range is small to prevent excessive shrinkage and porosity in die castings.
4) When superheat temperature is not high, it has sufficient fluidity to facilitate filling of complex mold cavities to obtain die castings with good surface quality.
5) Tendency of physical-chemical interactions with mold wall is small to reduce mold sticking and mutual alloying.

 

Aluminum alloy has low density, but relatively high strength, close to or exceeding high-quality steel. It has good plasticity and can be processed into various profiles. It has excellent electrical conductivity, thermal conductivity and corrosion resistance. It is widely used in industry, and its usage is second only to steel. Specific weight of aluminum alloy is only about 1/3 of iron, so it is very important in various industries. It plays an indispensable role in lightweight process of aircraft, ships, automobiles, electronic instruments, etc.
Commonly used ones are Al-Si-Cu series, and common ones are ADC12 (A383), ADC10 (A380), etc. There are also Al-Si series, Al-Si-Mg series, and Al-Mg series. In addition, what is currently called aluminum-titanium alloy is modified by adding titanium metal to above materials. Adding titanium metal can significantly improve mechanical properties of product.
National standard GB/T 15115 and Japanese standard JISH 5302 respectively stipulate brand, code, chemical composition, inspection methods and inspection rules of die-cast aluminum alloys.

Magnesium alloy is an alloy based on magnesium and added with other elements. Its characteristics are: low density, high specific strength, large specific elastic modulus, good heat dissipation, good shock absorption, greater ability to withstand impact loads than aluminum alloys, good resistance to organic matter and alkali corrosion. Specific gravity of magnesium is about 2/3 of aluminum and 1/4 of iron. Therefore, it is widely used in mobile phones, communication equipment and other electronic equipment, auto parts, and medical equipment.
Currently, magnesium-aluminum alloys are used, followed by magnesium-manganese alloys and magnesium-zinc-zirconium alloys. Commonly used grades include AZ91D, AM60B, AM50A, AS41B, etc.
With continuous improvement of development level of domestic manufacturing equipment industry, equipment level of die-casting machines has also been significantly improved, types of parts that can be manufactured are also constantly expanding, accuracy and complexity of die-cast parts have also been greatly improved. .
GB/T 25747-2022 Magnesium alloy die castings introduces grades, codes, chemical compositions, inspection methods and inspection rules of die-cast magnesium alloys, etc.

Zinc alloy has very good fluidity in molten state and has a low melting point of only 365 degrees. Various post-processing treatments can be performed, such as electroplating, etc. Therefore, it has a wide range of uses. It was also used a lot in mobile phone industry before. However, due to its large size and poor corrosion resistance, it was gradually eliminated by aluminum alloy. It is currently used in sanitary ware industry. Commonly used alloys are No. 2, 3, 4, 5, and No. 7. Currently, No. 3 alloy is used.
Relevant standard "Zinc Alloy Die Castings" is a Chinese national standard implemented on May 23, 2023. There is also GB/T 13821-2009 standard for zinc alloy die castings.

 

Cast copper alloys are divided into two major categories, brass and bronze.
Brass is a copper alloy mainly composed of zinc and alloying elements. In cast brass, other alloying elements are added to form manganese brass, aluminum brass, silicon brass, lead brass, etc. Copper alloys that do not contain zinc as main plus element are collectively called bronze, such as tin bronze, aluminum bronze, lead bronze, beryllium bronze, etc. National standards stipulate that there are 9 types of cast copper alloys, totaling 29 grades.
Characteristics of copper alloys
(1) Copper alloy has high mechanical properties, and its absolute values exceed those of zinc, aluminum and magnesium alloys.
(2) Copper alloy has good electrical conductivity and antimagnetic properties, and is often used to manufacture parts for instruments that are not allowed to be interfered by magnetic fields.
(3) Copper alloy has a small friction coefficient, a small linear expansion coefficient, and high wear resistance, fatigue limit and thermal conductivity.
(4) Copper alloy has high density, high price and high melting point.
(5) Die-cast copper alloys mostly use zinc (Zn) brass with a mass fraction of 35% to 40%. They have small crystal gaps, good fluidity and formability, and add a small amount of other elements such as: Pb, Si, and Al. , will improve cutting processing, wear resistance and mechanical properties of die castings.
Chemical composition and mechanical properties of die-cast copper alloy are mainly GB/T15116-1994.
In national standard, code name of die-cast copper alloy is named according to mass fraction of nominal component of alloy, and letters "YT" (meaning "ya", "tong" is the first letter of Chinese pinyin) are marked in front of alloy code, and text is added afterwards to explain alloy classification. For example, YT40-1 is lead brass, YT30-30 aluminum brass, and YT16-4 is silicon brass.
For further article, please refer to Die-casting design specifications—Introduction to die-casting mold technology.