As people's quality of life improves, the requirements for product aesthetics and quality are also constantly increasing. More and more consumer products are made of alloy materials. Metal materials give people a sense of high-end, solid and durable quality, while traditional plastic shell products are gradually labeled as "cheap" and "low quality" in the minds of consumers.

For consumer products, commonly used alloy materials are aluminum alloy, zinc alloy and magnesium alloy. Titanium alloy is often used in the medical field due to its good biocompatibility. Next, let's take a look at the characteristics of these alloy materials and make a comparison.

Therefore, the inductive summary is placed in front, see the following performance comparison table.

Physical performance comparison table

Of these four alloys, titanium alloy is the hardest and has the best strength. In terms of hardness, titanium alloy is much harder than the other three alloys. In terms of tensile strength, titanium alloy is stronger than zinc alloy, followed by magnesium alloy.

Strength and hardness comparison

However, for product structure design, weight also needs to be considered. If the specific gravity is considered, zinc alloy has the largest density and the smallest specific strength. Titanium alloy and magnesium alloy have high specific strength, but titanium alloy is expensive and has poor processability. Therefore, magnesium alloy is often used in structural parts that need to comprehensively consider weight and strength.

Aluminum alloy

You can directly find Baidu for material composition, so I won’t list them here. The density of aluminum alloy is 2.63~2.85g/cm, with high strength (σb is 110~270MPa), specific strength close to high alloy steel, specific stiffness exceeds steel, good casting performance and plastic processing performance, good electrical and thermal conductivity, good corrosion resistance and weldability.

Die-cast aluminum alloy has good fluidity and a melting point of 660℃.

Aluminum alloy has the most abundant process application forms in product structure design. Common processing technologies include: die casting, extrusion molding, machining, stamping, and forging. Aluminum alloy profiles are widely used in building doors and windows, and aluminum profiles are also commonly used to build frames for mechanical equipment. Aluminum alloys are also used in the shells of electronic products and fast-moving consumer goods. These products have high requirements for appearance, and the more common processes are extrusion, machining, stamping, etc.

The shell of fast-moving consumer goods rarely uses die-cast aluminum, because die-cast aluminum alloy contains a high content of Si, so when doing anodizing (anodizing), it directly reacts with the liquid medicine, and the surface effect after oxidation is relatively poor. Aluminum castings are often used for internal structural parts and parts with low requirements for appearance. The engine shell of a motorcycle requires a complex structure, light weight and sufficient strength. Most of them are rotated aluminum alloy die-cast as blanks.

Aluminum cast engine shell

Aluminum brand:

1. The series is: pure aluminum (aluminum content is not less than 99.00%), and the last two digits of the series brand are expressed as: the percentage of the lowest aluminum content. The second letter of the brand indicates the modification of the original pure aluminum.

2. The last two digits of the series brand have no special meaning and are only used to distinguish: different aluminum alloys in the same group. The second letter of the brand indicates the modification of the original pure aluminum.

2. The series is: aluminum alloy with copper as the main alloying element. 2011 fast cutting alloy, good cutting performance and high strength. 2018 2218 Forging alloy, good forging performance and high high temperature strength.

3. Series: Aluminum alloy with manganese as the main alloying element. 3105 3105 building materials, colored aluminum plates, bottle caps.

4. Series: Aluminum alloy with silicon as the main alloying element. 4032 has good heat resistance and wear resistance, and a small thermal expansion coefficient. Piston, cylinder head.

5. Series: Aluminum alloy with magnesium as the main alloying element. 5052 is the most representative alloy with medium strength, generally sheet metal, ships, vehicles, buildings, bottle caps, honeycomb plates.

6. Series: Aluminum alloy with magnesium as the main alloying element and Mg2Si phase as the strengthening phase. 6063 is a representative extrusion alloy with lower strength than 6061, good extrudability, can be used as a profile with complex cross-section shape, good corrosion resistance and surface treatment properties. Buildings, highway guardrails, high fences, vehicles, furniture, home appliances, decorations.

7. Series: Aluminum alloy with zinc as the main alloying element. 7075 is one of the alloys with the highest strength among aluminum alloys, but its corrosion resistance is poor. Covering with 7072 can improve its corrosion resistance, but the cost is increased. Aircraft, ski poles.

8. Series: Aluminum alloy with other elements as the main alloying elements

9. Series: Alternative alloy group

Aluminum alloys with a tensile strength greater than 480MPa are called high-strength aluminum alloys, mainly Al-Cu-Mg and Al-Zn-Mg-Cu based alloys, namely 2XXX (hard aluminum alloys) and 7XXX (super-hard aluminum alloys) series alloys. The static strength of the former is slightly lower than that of the latter, but the operating temperature is higher than that of the latter. Due to the different chemical composition, smelting and solidification methods, processing technology and heat treatment system of the alloy, the performance of the alloy varies greatly.

Common aluminum alloy performance table

Zinc alloy

Zinc alloy has a low melting point, good fluidity and is easy to weld. According to the manufacturing process, it can be divided into cast zinc alloy and deformed zinc alloy. Cast zinc alloy has good fluidity and corrosion resistance, and is suitable for die-casting instruments, automobile parts shells, etc. Deformed zinc alloy has good plasticity and ductility, and is mainly used as battery shells, printed boards, roof panels and daily hardware. The output of cast alloys is much greater than that of deformed alloys. For the structural parts of fast-moving consumer goods, deformed alloys are rarely used. Therefore, the following article only focuses on die-cast zinc alloys.

The density of zinc alloy is 6.3~6.7g/cm, the tensile strength σb is 280~440MPa, the melting point is low, it melts at 385℃, and it is easy to die-cast.

Zinc alloy has a large specific gravity, which is the largest among the four alloys described in this article. It also has the best fluidity and has good casting performance. It can die-cast complex and thin-walled precision parts, and the casting surface is smooth. In the product I designed, the thinnest wall thickness of zinc alloy die-casting is only 0.4mm.

At room temperature, the strength of zinc alloy is good. It should be noted that zinc alloy should not be used in high and low temperature (below 0℃) working environments. Zinc alloy has good mechanical properties at room temperature. However, the tensile strength at high temperatures and the impact properties at low temperatures are significantly reduced. Zinc alloys have poor corrosion resistance. When the impurity elements of lead, cadmium, and tin in the alloy composition exceed the standard, the castings will age and deform. Zinc alloy die castings have aging effects and aging phenomena, that is, the strength naturally decreases after a long time and becomes brittle. This is why many people complain that when replacing zinc alloy faucets, brittle fractures often occur, resulting in the faucet thread remaining in the water pipe and unable to be removed. Therefore, we still recommend that you try to choose copper faucets when decorating, not zinc alloy ones.

At present, there are two major standard series used as castings internationally, one is ZAMAK alloy and the other is ZA series alloy. The ZAMAK alloys used are ZAMAK 2, ZAMAK 3, ZAMAK5 and ZAMAK 7. (For simplicity, the above alloys are collectively referred to as alloys 2, 3, 5 and 7). The ZA series are ZA-8, ZA-12, ZA-27 and ZA-35. ZA-8 is mainly used for hot chamber die casting, while ZA-12 and ZA-27 can only be used for cold chamber die casting due to special melting requirements. ZA-35 is generally used for gravity castings. The development of ZAMAK alloy precedes that of ZA series alloys and is mainly used for pressure casting. The most widely used is zinc alloy No. 3.

ZAMAK 2: Used for mechanical parts with special requirements for mechanical properties, high hardness requirements, good wear resistance, and general dimensional accuracy requirements.

ZAMAK 3: Good fluidity and mechanical properties. Used for castings with low requirements for mechanical strength, such as toys, lamps, decorations, and some electrical components.

ZAMAK 5: Good fluidity and good mechanical properties. Used for castings with certain requirements for mechanical strength, such as automotive parts, electromechanical parts, mechanical parts, and electrical components.

ZA8: Has good impact strength and dimensional stability, but poor fluidity. Used for die castings with small size, high precision and mechanical strength requirements, such as electrical components.

Superloy: It has the best fluidity and is used for die-casting thin-walled, large-size, high-precision, and complex-shaped workpieces, such as electrical components and their housings.

Magnesium alloy

Magnesium alloy is an alloy composed of magnesium and other elements. The main alloying elements are aluminum, zinc, manganese, cerium, thorium, and a small amount of zirconium or cadmium. At present, the most widely used is magnesium-aluminum alloy, followed by magnesium-manganese alloy and magnesium-zinc alloy. Magnesium alloy can be widely used in automobiles, electronics, textiles, construction and military fields due to its excellent casting, extrusion, cutting and bending processing properties.

The melting point of magnesium alloy is 650℃, which is lower than that of aluminum alloy, and has good die-casting properties. The tensile strength of magnesium alloy castings is equivalent to that of aluminum alloy castings, generally up to 250MPa, and up to more than 600MPa.

Magnesium alloy has a low density (about 1.8g/cm3) and high strength. Magnesium alloy is the lightest metal structural material with a specific gravity of only 1.8, which is 2/3 of aluminum and 1/4 of iron respectively. Its specific strength is as high as 133, which makes magnesium alloy a high-strength material. The specific strength of high-strength magnesium alloys can even be comparable to that of titanium.

Magnesium alloys have a large elastic modulus and good shock absorption. Within the elastic range, when magnesium alloys are subjected to impact loads, the energy absorbed is half that of aluminum alloy parts, so magnesium alloys have good anti-vibration and noise reduction performance.

Magnesium alloys have good die-casting molding performance, and the minimum wall thickness of die-casting parts can reach 0.5mm, which is suitable for manufacturing various die-casting parts for automobiles. Magnesium alloy parts have high stability, and the casting processing dimensional accuracy of die-casting parts is high, and high-precision machining can be performed.

The heat dissipation of magnesium alloys has an absolute advantage over alloys. For radiators of magnesium alloys and aluminum alloys of the same volume and shape, the heat (temperature) produced by a heat source is easier for magnesium alloys to be transferred from the root of the heat sink to the top than for aluminum alloys, and the top is more likely to reach high temperatures.

However, the linear expansion coefficient of magnesium alloy is very large, reaching 25-26 μm/m℃, while that of aluminum alloy is 23 μm/m℃, brass is about 20 μm/m℃, structural steel is 12 μm/m℃, cast iron is about 10 μm/m℃, rock (granite, marble, etc.) is only 5-9 μm/m℃, and glass is 5-11 μm/m℃. When applied to heat sources, the influence of temperature on the structural size must be considered.

Examples of magnesium alloy applications: Generally, high-end and professional digital SLR cameras use magnesium alloy as the skeleton to make it durable and feel good; mobile phones, laptop shells; magnesium alloy is used on the shells and heat dissipation components of computers and projectors that generate high temperatures inside; automotive steering wheels, steering brackets, brake brackets, seat frames, mirror brackets, distribution brackets, etc. require light weight and high strength.

Magnesium alloy die-cast steering wheel skeleton

According to the forming method, it is divided into two categories: deformed magnesium alloy and cast magnesium alloy.

Magnesium alloy grades are represented in the form of English letters + numbers + English letters. The first English letter is the code of the main alloying element (the element code is specified in the following table), and the following numbers represent the average value of the upper and lower limits of the main alloying elements. The last English letter is the identification code, which is used to identify different alloys with different specific components or slight differences in element content.

Common grades of magnesium alloys include AZ31B, AZ31S, AZ31T, AZ40M, AZ41M, AZ61A, AZ61M, AZ61S, AZ62M, AZ63B, AZ80A, AZ80M, AZ80S, AZ91D, AM60B, AM50A, M1C, M2M, M2S, ZK61M, ZK61S, ME20M, LZ91, LZ61, LZ121, LA141, LA191, LAZ933, LA81, LA91, LAZ931, MA18, MA21, MA14, etc.

Titanium alloy

Titanium alloy refers to a variety of alloy metals made of titanium and other metals, with high strength, good corrosion resistance and high heat resistance. Titanium alloys are widely used in the production of aircraft engine compressor parts, skeletons, skins, fasteners and landing gear. Titanium alloys are also used in rockets, missiles and high-speed aircraft structural parts.

Titanium is an allotrope with a melting point of 1668℃. When it is below 882℃, it has a close-packed hexagonal lattice structure, called α titanium; when it is above 882℃, it has a body-centered cubic lattice structure, called β titanium. Using the different characteristics of the above two structures of titanium, appropriate alloying elements are added to obtain titanium alloys with different structures. At room temperature, titanium alloys have three matrix structures, and titanium alloys are divided into the following three categories: α alloy, (α+β) alloy and β alloy. In my country, they are represented by TA, TC and TB respectively.

The density of titanium alloy is generally around 4.51g/cm3, which is only 60% of that of steel. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloys is much greater than that of other metal structural materials, and parts with high unit strength, good rigidity and light weight can be made.

Mechanical properties of some titanium and titanium alloys

Titanium is non-toxic, light, high-strength and has excellent biocompatibility. It is an ideal medical metal material and can be used as an implant for human body. In the United States, five β-titanium alloys have been recommended to the medical field, namely TMZFTM (TI-12Mo-^Zr-2Fe), Ti-13Nb-13Zr, Timetal 21SRx (TI-15Mo-2.5Nb-0.2Si), Tiadyne 1610 (Ti-16Nb-9.5Hf) and Ti-15Mo, which are suitable for implantation into the human body as implants, such as artificial bones, vascular stents, etc.

TiNi alloy has good biocompatibility, and there are many medical examples that use its shape memory effect and superelasticity. Such as thrombus filters, spinal orthopedic rods, dental orthopedic wires, vascular stents, bone plates, intramedullary nails, artificial joints, contraceptive devices, heart repair components, micro pumps for artificial kidneys, etc.

Titanium alloy products can be obtained by die casting and machining methods. The melting temperature of titanium alloy is very high, and the requirements for mold steel are also high. There are many methods for machining titanium alloys, mainly including: turning, milling, boring, drilling, grinding, tapping, sawing, EDM, etc.

Titanium alloy machining performance is also poor. The cutting force of titanium alloy cutting is only slightly higher than that of steel with the same hardness, but most titanium alloys have very low thermal conductivity, only 1/7 of steel and 1/16 of aluminum. Therefore, the heat generated by cutting will not dissipate quickly, but will accumulate in the cutting area, causing the tool edge to wear quickly, collapse and generate built-up edge.