If you have been following mobile news recently, you might have noticed that a certain word has been appearing more and more frequently: titanium alloy. From high-end flagship phones to foldable screens, many manufacturers have started to use it as a new selling point. So, this seemingly "space-like" material, why is it suitable for use in mobile phones? Is it just a marketing gimmick? Today, we will use the simplest language to talk about titanium alloy and mobile phones.

What Is Titanium Alloy? What Make It Special?

You can think of titanium alloy as a "all-rounder". Unlike iron, it doesn't rust easily, and unlike aluminum, it is not as soft. It combines the advantages of several materials:

High strength

The common Ti-6Al-4V (Grade 5 titanium) has a yield strength of 900 MPa, which is three times that of 304 stainless steel. Therefore, the load-bearing capacity per unit mass is up to six times that of stainless steel. When a mobile phone drops, the frame needs to absorb 5-10 J of impact energy within 0.1 seconds. The high elastic deformation energy of titanium can absorb this energy without causing permanent plastic deformation, thereby reducing the probability of screen cracking.

Lightweight

This is the most attractive feature of titanium alloy. The density of titanium is approximately 4.5 g/cm³, which is much lower than that of stainless steel at 7.9 g/cm³. For mobile devices that need to be held frequently or placed in pockets, every 1 g reduction in weight can be immediately felt by the user. After replacing the stainless steel frame with a titanium alloy one in the iPhone 15 Pro, the overall weight decreased from 206 g to 187 g, a reduction of nearly 10%, while the bending stiffness remained basically unchanged. In other words, using it as the frame or casing of a mobile phone can make the phone both sturdy and durable without adding too much weight. If you highly value the durability and lightness of a mobile phone and don't want the frame to have scratches after using it for a while, or if you think the Pro/Ultra models are too heavy, then the weight reduction and reinforcement brought by titanium alloy are real advantages.

Corrosion-resistant

Many people are unaware that titanium is actually a metal with extremely good biocompatibility - it is often used for human implants, such as artificial joints and dental implants. The TiO₂ oxide film that forms on the titanium surface in an instant is only a few nanometers thick, but it can self-repair within the pH range of 3 to 11. Chloride ions (Cl⁻) are the "killers" that penetrate the stainless steel passivation film, but they have no effect on the titanium film. This means that taking selfies by the seaside, sweating during exercise, or wiping with disinfectant will not cause pitting corrosion, and the metal will maintain its luster over the long term.

Good appearance and feel

The unique gray color of titanium alloy does not shine as brightly as stainless steel, nor is it as plain as aluminum. The surface treatment can create a fine matte effect or a brushed texture. When held in your hand, it feels both solid and non-slip. You appreciate the unique material and the superior feel, and are willing to pay for this "quality" and "differentiation". Then, the titanium alloy body will not disappoint you.

Moreover, the thermal conductivity of titanium is 15 W m⁻¹ K⁻¹, only 1/13 of that of aluminum. In winter, holding it will not cause your hands to feel cold, and in summer, playing for a long time will not cause local temperatures to reach 45 ℃ like stainless steel. At the same time, the release of titanium ions is extremely low, and there are no common allergenic elements such as nickel and chromium. People with sensitive skin can also use it without wearing gloves.

The Mobile Phones Using Titanium Alloy

Titanium alloy is not a completely new concept, but it has only been widely used in mainstream mobile phones in recent years. Here are a few examples that you might be familiar with (please note that specific models and designs may change with version updates; this is only to illustrate the trend):

Apple iPhone 15 Pro series

Apple has for the first time used titanium alloy frames on the iPhone 15 Pro and Pro Max, replacing the previous stainless steel. The official emphasizes that this is to achieve the "best balance between strength, weight and feel", making the Pro models lighter in weight than the previous generation despite their larger size.

Samsung Galaxy S24 Ultra

Samsung also used titanium alloy in the frame of its flagship model S24 Ultra, highlighting its scratch-resistant and shock-resistant properties. Combined with the square-shaped body design, it further strengthened the image of "durability".

The frame and hinge of some foldable phone models

Some foldable phone models (such as some high-end models from domestic brands) have begun to use titanium alloy in key structural components, such as the phone frame and the hinge (the part that allows the screen to fold and rotate). Because foldable screens have extremely high requirements for material fatigue strength and thinness, titanium alloy has become the ideal choice.

Small-scale high-end or customized models

For a long time, some brands that are positioned as "luxurious" or "waterproof" have used titanium alloy to construct the entire body of their phones. The main selling point is extreme durability and a unique sense of identity.

Why aren't all mobile phones made of titanium?

At this point, you might ask: Since titanium alloys are so impressive, why isn't my mobile phone made of titanium alloy? The main reasons are:

High cost

The extraction, refining and processing of titanium itself are much more difficult than those of aluminum or stainless steel, which results in its high price. The price of titanium ingot raw materials is six times that of aluminum and 30 times that of stainless steel. This poses a huge challenge in controlling the overall cost of the machine, so currently only high-end models are willing to use it.

The challenging processing

Titanium alloys are very "hard" and also very "flexible". During the cutting process, the cutting tools wear out quickly, and the yield rate once dropped to only 30%. This places higher demands on CNC (numerical control machine tools) for cutting, grinding and shaping, resulting in longer production time and potentially lower product quality. In simple terms, it is both expensive and difficult to manufacture.

In the past two years, mobile phone manufacturers have used selective laser melting (SLM) 3D printing technology to manufacture small structural components such as hinges and lens rings, significantly reducing costs and processing difficulties:

• The material utilization rate has increased from <30% to >85%;
• Ultra-thin walls of 0.15 mm can also be formed in one go, and the strength has increased by 2 times;
• A large amount of CNC processing time has been saved, and the overall cost has decreased by 40%.

In summary, the introduction of titanium alloys into the mobile phone industry represents a meaningful exploration in the field of materials science by mobile phone manufacturers. It is not a gimmick created for the sake of new concepts, but rather a solution to the practical pain points of increasingly heavy mobile phones and the growing demand from users for durability. As technology matures and costs decrease, in the future, we are likely to see it on mid-range models as well. If your next mobile phone budget is sufficient and you are considering a high-end model that is lighter, more durable, and has a unique feel, then you might want to consider "whether to use titanium alloy" as a worthy reference point.